I've been running ARCs (24s on XC, 27s on AM) for a several years, and built a set or two for friends.
Pros:
- Reasonable price
- Reasonable weight
- Nice width
- Easy and reliable tubeless setup
- Welded seam
Cons:
- Soft (easy to dent)
I know all rims can be dented, and it is very difficult to empirically determine which rims are better, but anecdotally the original ARCs do seem softer than most other rims. The good side is you can typically just pound out the dents and keep riding.
The new ARC offsets are supposed to be a different more durable alloy but I have no experience with them.