I have been using a G&G M4 for the past 4 seasons, so far the only issues I've ever had with it is the tappet plate breaking(not a big deal, it's probably the the weakest part in any mechbox). That being said I have also heard a lot of bad reviews about G&G products. I can't speak for the newer CANSOFT stuff but I would buy another G&G in the future.
If your interested we are hosting an "FNG" day at the end of April and all are welcome to come out and participate. At the end of May we will be holding a sort of Milsim boot camp if you are interested in participating in Milsim games. On August long weekend we are hosting Operation Cold Front which is taking place at an old military base here in Manitoba.
Information for all these events and more are currently posted on http://www.operationcoldfront.com
Look forward to seeing you on the field this season.