http://image.noelshack.com/fichiers/2013/28/1373397789-ff-572-015.jpg
http://image.noelshack.com/fichiers/2013/28/1373397901-ff-572-016-017.jpg
You can see it is the same sled. And he has loads more than just that one gun.
Couple of factors here. Firstly, Etrigan is awesome but he does have verbal diarrhoea. Instead of instantly vaporizing Reed like he should do, he'd waste valuable melt-time with some fancy rhyming couplets. In the meantime Reed whips out the Supreme Demon-Destabilizer which he built in the last ten seconds out of an old toothbrush and some pencil shavings or some such BS.
Secondly, just because Reed is IN his lab, does that automatically give him auto-win? I mean, he still has to actually get to whatever ridiculous object is going to save the day. It's not like he actually walks round with the Ultimate Nullifier hitched to his belt like a Leatherman tool, is it?