Well, Get AV there are ton of ICS and G&G on sale.
I still always recommend ICS M4 than CA, It's just hard to find full metal ICS but once you find it then you won't disappointed.
A lots of people say that ICS M4 is not V2 compatible, For sure the gearbox is not compatible because of their split mechbox, easy swap for indoor and outdoor. The rest are almost identify to V2 mechbox excep the Anit-Reversal Latch. That's the part that can't change. The rest are pretty V2 mechbox.