We have one like this:
Kids would play on it intermittently, but it doesn’t take up much space. The triangle thing you mentioned looks really cool, probably lends itself for more active play, but a balance board works on a different skill.

For a 2 year old, you could consider a spooner board:
https://www.amazon.com/dp/B00WJJJX2Q?tag=verywellfit-20&linkCode=ogi&th=1&psc=1&ascsubtag=4172421%7Cnf90fa870dbdb4b638890116d440c691616

I think they have a floor model at barston’s childs play toy store if you want to try it out. Again it would probably be played with intermittently. I wouldn’t get anything without a non skid surface.

At two I also would wouldn’t get a half yoga ball or trampoline because toddlers knees aren’t as stable as when they’re older.

Does anyone have one of these and are they worth it? FWIW we already have a pikler triangle that my 2 year old loves. Wondering if both would be overkill?