The problem is this, copper tubing is ridiculously expensive at the moment, so everyone wants to use something else.
I design Industrial systems so my point of view may be differing a bit what what you where interested in.
Their are many things to consider, size of pipe, pressure, and type of installation. Some of my clients have suggested using stainless tubing, the problem here is that the installation cost is very high, (ie a butt welded connection is more time consuming than sweated fittings.)
HDPE is o.k. for low pressure stuff, but is in no way as durable, you sort of have to weigh the alternatives.
I would think for a buried water service less than 50 psi HDPE would be a fine application. Although you might need to think about how you would tie into the Main.