Why join a TA/Aux/Res unit? My goodness, one can be called on to do what they wear a uniform for! That is, to be activated on order and perhaps sent to war.... agree with the national commitments or not.
The personal commitment isn’t just playing soldiers on weekends and summer camps these days. The world and the threat has changed quite a bit lately, as has the capability of western nations to respond to it and influence the result.
Unfortunately, joining a “I’ll choose what I fight over and only in my off-season” force isn’t available. Those are only found in the mainland EU these days.
Reverserunlocked
You need to understand that putting the uniform on is a commitment. If you are willing to do what the uniform calls for put it on. If not don't. That said, all the elements you say you seek and more are found there.
Good luck