There are two flash carts, super everdrive and sd2snes.
Super everdrive is cheaper, but it doesn't support any games with special chips(only DSP in some cases), it lacks some fancy features like save states and loads roms slowly(reloading previously loaded rom is instant though).
SD2snes is the premium one, its way more expensive, but it supports superFX and SA-1 chips, save-states, loads roms very quickly etc.
As for playing SMW hacks, super everdrive works for everything that doesn't use SA-1 chip, but sd2snes plays those. There however are old hacks, that uses the old addmusicK that was piece of shit so those hacks only works on the zsnes emulator. Hacks that has either of those are clearly marked(I think) on the download selection.
I have super everdrive and all hacks I've tired plays no problem, some of them has some slowdown, or aren't designed with CRT overscan in mind, but for most part they aren't major problems(and the overscan issue varies a lot from TV to TV). Hack being vanilla or heavy-chocolate doesn't matter even on super everdrive, as long as its not using SA-1 or old addmusicK(broken music on newer emulators/flash carts).
Heres list of games with special chips in them
, in case you aren't familiar with it.