ISO 5355 is the standard alpine boot sole—the flat, rigid platform found on most traditional resort ski boots. If you're skiing exclusively at the resort and walking from the parking lot to the lodge is the extent of your off-snow travel, this is likely the right sole type for you.
The big advantage of ISO 5355 soles is power transmission. Because the sole is rigid and flat, energy transfers directly from your boot to the binding to the ski with minimal loss. That's why racers and aggressive resort skiers prefer them.
The trade-off is walkability. Alpine soles are stiff and flat, making them awkward and slippery for any real walking. If you want a boot that's comfortable to walk in around the village, look at GripWalk-compatible options instead.
Most standard alpine bindings are designed specifically for ISO 5355 soles, though many modern bindings now accept both alpine and GripWalk. Just double-check the binding specs before you buy.