I bought my R4 off modsupplier.com, only bought it since I don't have a pre-pay/debit card (COD is the only good thing for me anyhow.)
The newer shell for the R4 doesn't seem so great, considering there is no more spring mechanism (my older brother's friend got one for his b'day, I sneaked in when they weren't there to check out their computers a.k.a. LAN party), however, with the spring, there's always the chance that, when you drop it, it might break something.
If you want to get the spring-loaded one, you really should ask the stores, however, the newer one is standard now.