I expected these to fit and perform like the Baracudas I liked when i bought my Vipers. They didn't. I didn't like the fit and they were a battle to get on. Eventually, however, they molded to my feet and I got used to getting them on. Now I really like these shoes for gym bouldering. They fit well enough to use small feet and heel hook pretty dang well for a slipper. The cushion in the heel is nice as well. Good shoe, but it took me a while to be convinced.

Not the most comfortable shoe, but grips very well.

The last fits my medium with, flat (low volume) foot very well. The elastic closure strap runs over the full width and a length of nearly 10 cm, creating a very reliable fit, better than the "Cobra" or the Anasazi Slipper.

After some hours of use, the sole becomes soft and sensible. If the shoe was selected tight enough, you will still have enough edging power. The shoe will NOT stretch a lot - less than 1/2 size. I use 10.5 UK in street shoes and have this Viper in 42.5. La Sportiva's sizes are made in EUR, so half sizes allow more fine tuning than UK oder US half sizes.

As many La Sportiva climbing shoes, this also has a prominent stitching (seam) insind the shoe just over the big toe, which can result in some pain or skin fissure after a longer time of wear or when heaving damp skin.

I got these to serve as a more aggressive supplement to my much older Spires. They have now become my main shoes. The edging and smearing are incomparable; it's rare that a shoe excels at both. Hooking is good if the shoe is tight enough, but if you get them loose the heel could pop right out. They don't stretch at all. The rubber is durable and sticky. I would recommend these for most climbing styles; they're fantastic!

Great shoe, a bit hard to slip in (for my foot shape that is short and wide) but once on they feel like a neoprene sock.
Perfect for edges and holes, good on smearing, good foot support, very comfortable shoe. Great sticky rubber, very precise feeling of the footholds.
A must have for any La Sportiva fan.