The nano-flex armwarmers don't stay water resistant for long.
Yep! Mine are abismal even in the lightest shower. I think it is because the material is so thin that you don't feel insulated from the rain so still get cold and miserable (well I do ) which defeats the purpose of something supposed to be waterproof or water resistant.
I can see the Gabba as a good race option where you want to stay dryish but don't worry about getting a bit wet but I found the Santini H20 jersey more suited to my needs. Very waterproof for what feels like a normal top. I use a windproof tee underneath when the wind picks up. If used under a light hard shell then you'll be absolutely bone dry even in the worst that Winter can throw at you (much prefer this approach to one big heavy winter jacket). Basically, super versatile to be dressed up or dressed down and more waterproof than I found the equivalent Castelli materials
Edit: There is a good thread on Weightweenies about Gabba experiences with lots of cheaper options using the same materials and general alternatives. Cheapest option was a short sleeve tee listed for diving at Decathalon which people seemed very happy with IIRC- could get quite toasty though!