20 kN wrote: For the most part, they are only useful in flairs and pinscars. They are specialty pieces.
All depends on where you frequently climb. Some areas have very few flaring placements and there, yes, Offset cams can be a specialty piece. Other areas however, eat up Offset cams. Yes, Yosemite Aid routes are the classic example but there are many, many more places where I've loved the offset cam. I actually consider it a MUST HAVE piece for nearly all free climbing and it's the rare area where I DON'T bring at least a few offset cams. On a free rack you'll really only have 3-4 anyway.
Off the top of my head, I've loved offsets in : Squamish, Index, WA and other granite of WA, Lumpy Ridge, Lovers Leap, Yos., J-Tree (awesome there) and Taquitz. I've used them in Red Rocks but not as often.
I've owned and used both the Metolius and Aliens. (both CCH/Fixe and Totem) On the really smooth granite (Yos) I think there is a difference and the softer Alien lobes "bite" just a bit better. On rougher textured rock (J-Tree) I never thought is was that big a difference.
If you're just looking for a few cams to supplement a Free rack 3 Fixe or Totem offsets (B/G. G/Y. Y/R) are your best bet. If you're looking to double up on smaller sizes (maybe you only have singles ) and you climb in areas that tend to have the pods and flares a run of the Metolius Offsets would be worth considering. In J-Tree I run a set of Met Offsets 00/0 to 1/2 because there are LOTS of flaring placements there.