I've shot a unitec on both my Ion's, usually in either a .689 or .693 bore. Perform really well, giving good accuracy/range for average quality paint. They are also very quiet, and lightweight compared to some other barrels.
I have had a .689 on my PMR for nearly 2 years now and i have never had any problems.. have hit the ground barrell 1st a couple of times and no signs of damage at all.
Great barrell sets for the price!.. going to be getting another one very soon..
read lots of good stuff about these barrels so am ordering one of warped. thing is my card wont register with them and want to pay with paypal but the havent replied