I was a pretty heavy user of Communauto, until recently. I had the heavy-usage plan.
What I didn't know was that after a year of being charged monthly, I would be switched to the "open" plan (no plan, essentially). This results in trips which would normally cost 10$ costing 50$. The resulting massive bill was a surprise, and after a year of faithfully paying I expected it would be a small thing to reinstate the plan I'd always had, and adjust those dozen 50$ trips to the normal ~120-150$ total. Nope! The 600$ bill is considered entirely my problem.
Total cash grab with a predatory billing practice. Never in my life been so throughly ripped off by a company.
If you are thinking of signing up, I highly recommend you think again.