Confirming other's replies... yes, the clip is easily removed. It's the first thing I did on my Jet I Pro IBS v3.0.
Removing the clip is the first thing I do with nearly all of my lights, as the clip is pretty much "in my way" when hand holding most lights, most of the time. Guess I'm just not a clip fan!
As for comparing to the Quark. I would choose the Quark over the Jet I, as the Quark has a better general-use beam, wider, cleaner spill, a much lower low, and is infinitely more modular (let's say "mega-lego-able") allowing use of a CR123/RCR123, 14500, and 17670 battery tube with the same head and tailcap. That's super sweet versatility!
I do like my Jet I Pro IBS v.3 as a pocket thrower, where with SMO reflector it does slightly exceed the Quark - strictly for throw. But for pretty much all other applications, I'd prefer one of my Quarks, as they have such a cleaner, wider, and much more beautiful beam, almost as throwy as the Jet I, but much cleaner beam, and far more versatile as for powering/battery tube options. They're both very nice lights, but as an owner of both, the Quark gets my vote.
When Jet comes out with a Jet I Pro with an XP-E R2 emitter, my opinion
may change... we'll see. Until then, for me... Quark AA easily edges out Jet I Pro IBS v.3.