The Cocoweb Armbar Combo surprised us. We didn't expect it to be easy to use, but it operates smoothly and on par with high-end models. We couldn't imagine it was secure, but it resisted defeat against all hand tools, only succumbing to the power of the angle grinder. Its versatility is great when you use the cable to lock up the saddle and front wheel without removing them, too. Our main complaint concerns the mount, which is inferior to other models. For $30, you don't get the key replacement or theft protection programs that come with models from Kryptonite, but you do get a legit U-lock that fulfills most biker's needs.
A comparable lock we reviewed is the more convenient Kryptonite Kryptolok Series 2 Standard U-Lock. It's easier to use and comes with a widely-accepted independent security rating. For a low price with more manageable portability, check out the INBIKE 8 Joint Folding Lock. The lock has less weight but is also less secure.