If you're going to add water shut-off, your best bet is to go with one that rotates a ball valve, not a solenoid that operates a diaphragm for your main. The leakSmart valves are very nice because they also have a built-in battery backup and there's a community driver that works. I have one and a few other here do as well. Some were had via the Lowe's clear out and some are getting them from ebay for as little at $30 and that's quite good for a valve that retailed at Lowe's for $159 originally and well over $250 average from Waxman.
If anyone is going to buy a valve from China, please keep in mind that putting them on your water main may not be safe. Not all sellers disclose that their valves contain materials that are not safe for drinking water. Some do though, and offer valves that are safe for use with potable water.
For the OP, this wouldn't have helped, because the issue was a powered sump pump. But a simple smart switch could have been used to power off the sump pump automatically when the leak was detected. You're quite lucky that the leak hit the sensor and notified you.
