Schnarph, you don't have to rationalize getting a voltage meter if you use mechs. It's for your and your battery's safety. There's no other way for you to tell if you have over drained your battery on the fly other than the "feel" of the hit. You always should be aware of your battery's charge state as well as be able to diagnose flaws in your builds. I wouldn't advise using the sigelei #20 for sub-ohm vaping. I really don't have faith in that switch. Both the build and the materials used are questionable to me. I haven't been in the sigelei thread in a long while, but I bet it's a pretty difficult thing to modify up to fail-safe specs. Plenty of inexpensive mechs out there that do the job very well.