We got one free as a hand-me-down, so they don't have to be too wasteful.
I currently find it useful for two things:
1) Middle of the night: we leave the potty in the bedroom and it seems to cue him to actually get up and pee (or, more often, tell us that he needs to pee so we can help him) instead of wetting the bed (which was happening way too often before).
2) We only have one bathroom, it's good to have the potty handy if kid needs to go NOW and one of us is using the toilet
Initially, we had an insert/adapter and TBH, I found it a bit of a pain. Whenever kid wants to go, you have to go in and get the adapter on the toilet for them. Initially they may not be able to hold it for long, so the 10 seconds you spend slapping the adapter on can actually be critical. Also, for the first few days you may be putting your kid on the potty a LOT, taking the adapter on and off over and over again is annoying. Now I mostly just plop kid on toilet with no adapter (he's pretty big though, so I have zero concerns about him falling in). So the adapter was actually the more useless option for us.
Our son also did settle into a poop 1x/day at about the same time every day routine pretty quickly after potty training, if I know he's at a time when he's likely to poop, he goes on the toilet, so most of the time all we are cleaning out of the potty is pee, which is clearly pretty simple. Cleaning poop out of the potty is definitely not on my list of fun things to do.