*PLUMBERSSTOCK EXPERT* responded:
Hi, there! Thank you for inquiring with us. For the most part, the only difference between brass and poly alloy (plastic) would be the materials being used. Both fittings are designed to be installed using the crimp, clamp, and steel clamping methods. Plastic is lighter is mostly preferred for water applications where water is very acidic or you have contamination concerns where brass does not react well. Brass, on the other hand, is pretty common and is the most standard fitting being used. In the end, it really comes down to preference and other factors along with the local codes that you need to follow. Hope this helps. Thank you for visiting us here at PlumbersStock.com!