I only use the waterworks compression fittings in rare instances. The fact that they get used to set water meters on copper supply lines, where flared fittings were used in the past, is a testament to their reliability. On sprinkler zone lines, I expect ordinary FloSpan compression couplings could handle most duties.
There is an ancient sort of 'poly pipe' I've seen that might be similar to your pipe. It was a bright green, was connected with insert fittings, and reacted oddly to blowtorch heat when repairing it. It almost had a 'candle wax' feel to it when softened. It also would split crosswise, instead of the usual direction of poly pipe splits.
I know how it can be with tools. I bought a Buckner nozzle wrench online, just to have it.