You have to be really careful with the SMPL, as it doesn't have the traditional top cap with positive pin. There's some info in this thread:
https://www.e-cigarette-forum.com/forum/threads/a-smpl-explosion.677217/ If you're OK with ALWAYS taking the necessary safety precautions, it's a really nice mod. I don't own a Nemesis, so can't say anything about those.
The switch is a little crunchy on the SMPL, so it would need a little sanding and finessing. Most people have preferred the version with the retainer ring, not the screw. Don't get the black one. I was able to scratch the finish off mine with my fingernail, all the way down to bare brass. There's a 1:1 clone at FT, for around $17. If I were to buy another one, it would probably be that one.