I still have 2 toptank mini's out of the original 4 I bought, they are top or bottom fill your choice, vape the same as a stm. I usually use the .5Ω Clapton head.
Nothing new about them, I've had them for a year or more.
IMO, no more prone to leaking than the stm, one of mine has been sitting filled for at least 3 months, hasn't seeped a drop.
The only down side I can think of is the seal kit is supposed to be different from the stm, which makes sense considering the top cap has 2 seals on it.
Haven't found a local source for the seal kit which is fine because I haven't needed to replace any seals.
I know the clone top tanks are prone to leak & have a habit of cheesing up the top cap seal to the chimney, causing leaks, some wicking & liquid in mouth problems.