VSS snapshots are SQL consistent and the feature no longer requires SQL Enterprise. They are supposed to be very fast - they may not be fast without adequate maintenance, but thorough maintenance is just a non-optional cost of an instance such as that. I have only had them either function normally, and quiesce for a few hundred milliseconds at most, or not function at all and quiesce for dozens of seconds or minutes. (cough veeam, cough snap manager)
I cannot even begin to imagine having a recurring 12-hour maintenance window to run backups. I suppose if I did I would prefer traditional backups but I have never had that, even in my "8-5" shops.
What kind of maintenance are you referring to?
Have you ever had the IO being frozen cause an issue with a system from a VSS snapshot? I have.
Have you every thoroughly tested the data consistency (loss) from a snapshot of any type? I have.
Have you ever had to recover (in the middle of a disaster) from a snapshot and have it fail? I have. Thankfully I had a tried and true backup and recovery process in place.
Have you every had a snapshot bring a system to it's knees, or take it completely offline? I have.
Sorry, I have had more issues with snapshots of various kinds over the years when you needed them most. To RECOVER. It's not a backup strategy, it's a recovery strategy.