Hello! So for christmas I got money for buying a chain, I already use the OnGuard Pitbull mini DT u-lock and haven't had any problems; it's just that it can get really hard to find a suitable locking spot, bike racks are not common in this country yet; many times I end up locking the bike to a metal fence that really does seem weaker than the lock itself because there's nowhere else to go . So, i'm getting a Pragmasis chain (https://securityforbikes.com/security-chains.php) long enough to go around an electricity pole. My main question is, is it worth it to go with the 13mm one? or is the 11mm good enough for bicycles? i don't think bike thiefs in my city are using angle grinders of 4ft bolt cutters yet but i don't want to spend the money on the 11mm one if it's really not good enough. Has anyone had a bad experience with an 11mm one?

Merry christmas to all

Looks like a good strong chain to me. Any lock is really only providing deterrence and the 11 mm looks like it would do that well enough. I don't have experience with the chains you're considering though.

Go for what you can afford. The bigger the better.
If you intend to use the 13mm mini ulock to lock the chain then no need to go over 13mm.
There are several brands oxford, al max(>15mm), kryptonite, abus etc..
No need to go for longer chains than 1.5m to avoid gaps
a 1.2 or 1.5m long chain should be perfect