Yes, they are. It's a shame when you try to buy some things and why you end avoiding some good online shops. Getting cheap batteries is not that easy if you live, like me, in Spain. That's why I smile when someone states that CR123 lights are "better" because you can find them cheap online (If you want to get a reputable brand).
Back on topic.
The first thing to note is that I am a big fan of 2xAA format. I think they are the best compromise between runtime, easy to handle, size, battery type, lack of maintenance (think of average joe with li-ions), etc. If some friend ask me about what kind of light to get for "normal" use, I will tell him to get a 2xAA one. Of course, there are situations where another form factors are more recommended.
I have both Fenix LD20 and Quark 2xAA (warm). There are a couple of differences between them, although not of them objetive, that should lean you towards one of another.
Both of them are quality lights, but the Fenix
feels better in the hand. Of course, that's my own opinion/taste. Some complain about the LD20 being slippery, but in my hand it just feels great. The anodized in the Quark started to wear out a bit in the Quark knurling and seems thinner than in the Fenix (I got the Fenix several months before the Quark and there is no sign of wear yet).
I found the threads in the LD20 a bit too thing. Sometimes is a bit hard to start screwing the tailcap after a cell change, but they are anodized both in the tailcap and the body. The quark ones are only anodized in the tailcap (remember, I have the "updated" tailcap wich came with the warm versions) and that can lead to lockout problems, but as I never use it, for me is not a concern.
The switch in the Fenix feels better to, even if the warm Quarks came with the updated-and-not-that-hard-to-press switch. I am not saying that the Quark swith is bad or something like that, but I like the L20 more. Another thing I dont like in the Quark is the battery rattling (not big, but it is there), wich is not present in the Fenix. The Quark have a reversable clip too.
The Quark can tailstand perfectly. The tailcap end is totally flat (regular version) and feels very secure in that position. Yes, the Fenix, can tailstand too... if you like doing equilibrium games. You need a perfect and flat surface to do it, but if you breath too strong near it, it will fall down. I have to note too that the lanyard holes are good but not perfect. If you use the tiny split-ring (included) in one hole, you lose the tailstanding feature, but if you use the two holes, the split ring stumbles against the boot tail and the resulting position is a bit "intrusive" (sorry, but I dont know how to explain this, I am lackin vocabulary here). I think they should redesing it and get something like the Nitecore D10/D20.
But the big, big difference is the real low modes that the Quark have. You get a "moon mode" that its perfect for keeping your night-vision intact (or your wife asleep) with GREAT runtime and the different brightness levels are "better" IMHO. The Fenix "Low" is almost as bright as the Quark medium, but the maximun one is comparable in both. The LD20 have "cree rings" whereas the Quark is flawless (almost perfect, in fact).
I think it summarizes more or less the differences between them. My LD20 is right now almost a shelf queen after getting the Quark (I really like the low modes). If the hipotetically friend I talked about asked me what to get, I will probably say, get a... Fenix TK20
crackup
.
Why? Average people only use flashlights when they need a decent amount of light and for relative short periods of time. The beam pattern/throw is more like the one in the usual incans (tint too) and is almost indestructible.
Edit: OMG, the reply was HUGE.
