Miss the thumb loop. For me having a thumb loop is helpful at times extracting a cam. I'll be moving away from Master Cams when I need to replace / add small cams.
Thumb loop - Can clip while aiding for an extra couple inches. Some find it easier than the not thumb loop to find while placing Harder to find as only old cams have it
Not thumb loop - Some find it just as easy to place (I do) Can't get extra few inches aiding Easy to find and can buy new Slightly lighter than thumb loop
I use both Fixe Aliens and Ultralight Mastercams. I'm kind of neutral I guess, they supposedly took it off to save weight, right? I like the weight and space savings, but I do find I have to fiddle with the Mastercams more than the Aliens or other looped cams during placement.
I feel like the ultra-lightness, decent cost and fine quality outweigh the lack of a loop for me. Seems like Metolius would have a really awesome cam if they put a totem-style loop in the middle of the sling or something like that!
I actually prefer the no-thumb-loop design of the Metolius ULMCs. They take up far less space on my harness and they are easier to place by putting the butt-end of the cam into the meat of my thumb muscle.