I sail my 16 solo on a regular basis just using a righting bag, but you're right it can be difficult to use, simply because while the boat is on its side you have to unroll it and then fill it with water and lean out. I haven't used a pole myself. If the wind is up around 20mph, I can usually right it without a bag because you get a lot of help from the wind, but under 15mph solo you have to use an aid.
I'd say if I were you to qualify someone to take a h16 out solo, I'd go out with them once, capsize it deliberately, and make them right it solo. I'd also have a safety boat on-hand just in case. And maybe get some waterproof walkie-talkies so that someone can call for help if they need it.
I've only *not* been able to do it alone once and that incident is detailed in the H16 forum. Basically there was very little wind so I didn't bother bringing the righting bag, then the wind picked up for a few minutes, capsized me, and then died down again.