I actually found a Piranha Alpine Knife while climbing the Kain route on Bugaboo Spire and ended up using it for the rest of the trip. Previously I’d used a very small Gerber knife with a 2.5″ locking blade. The Trango is nicely designed and very small. The blade had an ingenious mechanism to lock it when open and relies on the biner to prevent accidental opening. It also includes a bottle opener. After some use I concluded that the knife’s small size doesn’t actually count in it’s favor.
The knife on my harness gets used for all sorts of things from cutting ropes to slicing cheese. The Piranha’s blade is actually very short, fine for cutting rap anchors but not much use for anything else. While you can open it one handed the knife’s very small size make this hard to do, especially with gloves on. I certainly wouldn’t want to be building anchors with this while retreating off a winter route.
My real problem with the Piranha is that you have to take it off the biner in order to use it. The knife is designed to be stored on a biner and this keeps the blade locked closed. This means you can end up dropping it, especially if you’re wearing thick gloves. My old knife could be used while still safely clipped to a sling so there’s no chance a dropping it while setting anchors.
If all you do is cragging and want a knife on your rack then the Piranha might fit the bill but for more serious use on large alpine routes and multi day trips I’m sticking with my existing setup. As for the bottle opener, I’ve never met a bottle I couldn’t open somehow.