This was an amazing experience! Since this was our first time boating solo and our first time to Bora Bora, here is a detailed, objective review - hopefully it helps.
We ended up doing it 2 days in a row - the first day on the 6hp Quintrex boat (no license required) and the second day on the 30hp pontoon boat (license required).
The people: The owner, Frank, and all of his staff were so friendly, warm, and helpful. They were very communicative when we had questions in advance through Viator. Once we got to Bora Bora, Frank was right on time to pick us up both days in a row and very kindly even accommodated a pit stop on the way so that we could stop at the grocery store. The office is located in the Maitai hotel and is very nice - also great that it is right across the road from the actual beach/boats. One of his staff, I think Jeff, who explained all the rules and recommendations to us, gave an excellent explanation and was also very funny. Frank and his wife have been on the island for well over a decade and were really great to chat with.
6hp Quintrex: We got a boat license ahead of time based on one of the other comments and emphatically recommend it so you can get the 30hp pontoon (course was very easy, costed $10 through our state of California and it did take 4 hours or so but you can multitask and break it up). However, the first day the 30hp was booked (perhaps we should have reserved it ahead of time but didn't think to do so) so we took the 6hp Quintrex, which is the little orange boats in the photos. It was just big enough to fit the both of us and definitely was not very fast, though we didn't think it was as slow as some other reviews seem to have felt. Since it was our first time operating a boat ourselves, and that day it was ~20mph and somewhat choppy, we didn't venture too far. The recommended route is counterclockwise, so the Maitai hotel is at 6 o clock and you work your way backwards around the island. There is an L-shaped motu that forms the right side of Bora Bora (Piti Aau), and we hung out on a very, very nice beach there and had it basically to ourselves, except some adorable and sweet stray dogs to whom we donated half our food. It only took about 20-30 minutes to get there.
30hp Pontoon: This was the true experience! It was a lot roomier, felt a lot more stable, and went way faster. It was definitely worth getting the license for! The wind was about the same that day, but things felt much safer and more manageable on this boat. We went all the way to the halfway point (Motu Tevairoa), but it was quite windy and choppy on that side even on the beach, despite it being shallower. We didn't feel too comfortable staying but there was also little appeal to. Given all that, and there aren't as many recommended stopping points on the second half of the island, we went back east to an amazing, very calm beach between the Four Seasons and the St Regis (our favorite beach on the island). It did take us longer to go backwards because we were working against the current, but it was still only about 30-40 minutes from the Conrad back to the Maitai.
Safety: Overall we felt very safe on both boats, even despite the wind, but you do have to use your common sense and stay aware and we would say this experience is not for everyone (and probably not for children). With the smaller boat, we would have felt uncomfortable on the airport side with the waves/wind (they don't rent these boats on certain days because of this). FYI, the current/wind comes from the southeast, so it doesn't seem like it's possible to accidentally "drift out of the lagoon" on that side (maybe the airport side though). That said, definitely pick the places where you swim very carefully regardless of which boat - the current can be very, very strong, especially at the southeast (which is where people snorkel for rays/sharks) and northwest sides. It's a lagoon, but it's still open water! Because of this we opted not to stop at coral gardens, but lots of people stop there so maybe it isn't that bad. And the water is very deep in the middle of the lagoon. On the plus side, there are lots of boats out, so it would likely not be hard to spot you in the water if you need help provided you have a life jacket on. The company also provides a radio phone, life vests, and a map of the island with the route, recommended stops, and areas to avoid marked out very accurately. I think we had internet at all points, but just in case, we HIGHLY recommend downloading a Google map of the island so that you can track exactly where you are on the company map and make sure you are staying within the right areas and aren't getting near coral (there are some forbidden areas you have to stay out of to avoid damaging coral/getting stuck). With the current/wind and a small boat/engine, it's important to monitor your course. We had Google maps up continuously when on the move. We didn't have any issues with boat traffic - there were lots of other, larger and faster boats in the lagoon but they give you a wide berth.
Tips: As others mentioned, the company provides a cooler and ice, but it saves time to go grocery shopping the day before if you can. Chin Lee has all the basics - we got sandwich ingredients, chips, and water. You can also rent snorkel gear at the office if you'd like.
Time/Duration: We stayed out the entire day both days (~8:30-5). On the Quintrex more time is devoted to travelling, but by staying close we got to enjoy a lot of time in one spot (which was so good we didn't feel the need to move). On the 30hp, we stopped briefly at 3 spots and stayed for several hours at a fourth spot, and got back right at 5pm. If you don't want to stop much, you probably don't need the full day (they say it takes 1 hr to travel the diameter of the island in any direction, I believe only with the 30hp though).
Overall, we had an amazing time and having the opportunity to go out on our own was very unique and special. If (or rather when) we come back to Bora Bora, we will most likely do this again. Thank you La Plage!