Rehau are a German brand and very good quality. They also have a pre-insulated range and well priced. The downside is that you must purchase special inserts to connect to Irish fittings, priced at €1.80 + VAT each. Does not sound much but if you add up the cost of 3 per tee, etc. it adds a lot to the cost. The pipe bends lovely and is very rigid so no sagging when hot like Qualpex. It is also white so rising to radiators is a nice finish.
Qualpex also do a pre-insulated pipe and it goes straight into Irish fittings with an inexpensive insert. Not rigid though.