Not all 18650s are the same size, so be careful...i have wrecked a REO by forcing a protected 18650 in it and fusing it.
If you are after a decent, reliable mod that never fails then i'd suggest a Silver Bullet - $84 from
AltSmoke.com | Personal Vaporizers | Electronic Cigarette | Ecigs | Your one stop shop! - they don't have the push down activation but they go some. a 510 connection means anything fits in it - it really is becoming the standard now.
I typically run a tank on mine - a Vivi Nova, but i also have some rebuildable atomisers that work just fine too - if you drip.
It's not expensive and you can drop it and it makes no difference.
T