0.25 to 0.5 is perfectly fine with any mech and true 20a cdr cell... The conservative limit for a true 20a cdr cell is 0.25 and above(0.2 ohms at 4.2v is 21a).
Imho, the most important thing with mechs, besides of course to not build over the battery specs, is very importantly to know what to do if something fails... I mean, if a fire-button gets stuck or other malfunction internally(i've had that several times, by tinkering with lowest throw possible e.g.), then if you're the type who just throws away your mod on the floor and get scared, then imho, mechs aren't for you(not you, generally I mean

)... One needs to understand that malfunctions can happen and what to do about them... Either you quickly drop/loosen the cell(s) or take e.g. a paper-towel and quickly screw atty off/loosen... That's what I always do... Also, I newer leave "loaded" mechs unattended and so take the cells out of all of them, before going out... When going out, I just use a mech with a tank and pretty high build to avoid dripping while out and avoid having to carry too many extra cells... I DIY so make a little extra strong mix for going out/tanks...
Everyone, if you don't DIY already then I highly recommend starting... It's extremely more cost-effective and you're in complete control additionally...