Well, all of the Chinese-made APVs suffer from cheap, under-spec'ed switches and the Innokin SVD is the worst of them all. It has three undersized and weak switches.
Both Vamo and SVD do the same work as the Sigelei Zmax V3 and V5 telescopic tubes mods but are significantly longer in size than the Sigeleis. Both Vamo and SVD have soft chrome-plated brass 510/eGo threading while the Sigeleis have a one-piece stainless steel 510/eGo threading assembly.
However, the single switch on the Sigeleis isn't the best, either. It can crap out in a couple of months, several months or over a year later even if the 510-eGo threading is darned near indestructible. Buy a Sigelei and you are rolling the dice on switch life, just like any other Chinese-made APV except you are only rolling the dice once instead of three times.
The good news is that the Sigeleis only have one switch to fail. And it is not undersized like the Innokin SVD. And if you are a Tool Time type of guy and can use a workbench and a soldering iron you can replace the Sigelei switch yourself with a replacement third party switch rated for one million click cycles for as little as 74 cents. If you are tool-impaired and helpless, then buy a Provari and pay them to fix their switch when it fails.
Sigelei switch replacement