<deep breath....and GO> as a D1 we were forced into buying surgitel loupes because they came as part of our instrument it and, well, we really didnt know any better. as a current D4, i can say with confidence that the same pair of loupes i got waaay back in my first year now do a great job of holding up a hook on the left side of my locker in a fairly permanent manner.
flip-ups, particulary surgitel, blow monkey nards. (is that even permissible!?) field of vision, neck angle, ease of adjustment, blah, blah, blah....thhppppp! the real key for my dissatisfaction was all the freaking moving parts. all the little teensy, weensy freaking screws. a year and a half of pre-clinical labs, and my loupes were sliding down the track on the (heavy) frame and literally tipping forward off the bridge of my nose. sure, the rep came by the school every few weeks to tighten and tweak all the loose bits but, seriously, if the rep has to come fix things that often, how well made is the initial product? exactly.
do i wear loupes? you bet! i love being able to finish the margins of a composite or bevel a crown prep without having to invade more of my patients personal space than i already am...but for my (own) money, i bought a pair of TTL from designs for vision. custom made for my exact eyes and comfortable working length, tons lighter than my old flip-ups, both due to reduced lens bulk and titanium frames. best of all, there are NO moving parts. no flip-up apparatus to maintain, no interpupillary distance to adjust everytime you take them off and put them back on. nothing but put them on and get to work. the same feel everytime, the same working distance, perfectly fitted to me.
<whew> so, in conclusion, if you have choice, seriously consider TTLs. see if you can get to a dental show and try on a bunch of different vendors. orascoptic and DFV are the major players, but there are several oter folks out there. i would stick with 2.5x to start with and stick with it...there is a learning curve to using loupes. my opinions come free of charge if you have any other questions...