My experiences are as follows:
1. I started solo diving a long time ago in the Pacific NW because I didn't have enough buddies who wanted to dive as often as me or didn't have the availability to dive as much as me (all of my buddies at the time were other divemasters and instructors who spent all of their time working with students and didn't fun dive).
2. I only solo dived locations that were completely familiar to me and had zero hazards. I dived with common sense and redundancy equipment, but no "formal" training cert.
3. I have dived solo on Grand Cayman and Bonaire many times without a solo or self reliant certification.
4. Bonaire is much easier to do so and as others have mentioned, if you don't make an issue about it or bring it up, nobody else will likely do so either. I have rolled into Dive Friends with the pickup by myself and loaded 8+ tanks at a time for me and my group without anyone saying a thing. I grab tanks from any of their locations before they close, by myself, and no one says a thing. I go out night diving or dawn diving and no one says a thing.
5. I have stayed at Sunset House on Grand Cayman numerous times and same thing. I grab tanks before the shop closes and throw them in my locker and do a solo shore night dive or dawn dive and no one says a thing. Don't ask, don't tell.
6. I did decide to get my PADI self-reliant certification, just to have it for any future issues on liveaboards or other dive destinations. I ended up getting my cert in Bonaire and with Dive Friends. I absolutely loved the class and had a great time. As experienced as I thought I was and despite how much I thought I knew, I learned lots of things and don't regret for a minute the $$ spent. Of course, I had an outstanding instructor, so I wouldn't necessarily guarantee that for everyone.
7. You can rent a pony from Dive Friends if you have the solo or self reliant certification.
8. Prior to being self-reliant certified, I was able to rent a pony tank at a very reasonable rate from the TDS shop at Captain Don's Habitat and they never asked to see any cert card. I assume that is still true--
Technical Diving Services - Captain Don's Habitat - Bonaire
9. In a past life, I raced mountain bikes, road bikes and off-road motorcycles competitively and trained solo all the time. I would go on 9 hour training rides in the Oregon Cascades backcountry on my mountain bike with nothing but myself, my bike and some redundant gear (tools, spare tubes, patches, enough water and food)- I find it interesting how different sports and activities treat solo participants differently.
I could go on, but 9 bullet points is probably enough for now.