The answer is in the name there are many MS polymer sealant/adhesives on the market with varying levels of quality resulting in performance. The next grade up is a Hybrid polymer with the same varying qualities and performances the Wickes Premium Hybrid...

Solder ring Fitting Reducer (Dia)15mm x 8mm.This fitting reducer from Plumbsure has a durable copper construction. It is fitted by heating until the solder runs around the joint by capillary action.