I had some existing Xiaomi Mijia and Aqara sensors from the old house. In the old house I had started to use Home Assistant with Home Assistant Device Bridge to bring devices into Hubitat for Automation. That worked so well, that I bought a RPi and setup Home Assistant Supervisor with Z2M and a Conbee 2 Zigbee controller in the new house. Very happy with my decision. My devices were inexpensive, they're small, batteries last a very long time and they perform perfectly. A few of my non-xaiomi sensors are directly joined to HE and they work great too.
It's a mix of Aqara, Leaksmart, Thirdreality and one Insteon. All are connected to Hubitat direclty and all work fine. I'd protect your investment with something more than just leak sensors and an automated valve. I have a Leaksmart valve that I never installed because when we moved into this house, it had polybutylene pipes. We couldn't get a plumber in for about 8 months, so I bought Moen Flo. The plumbing has now been replaced with PEX, but I'm glad I have Flo. It has caught toilets running on and leaking hose bibbs. Couldn't have found that with a leak sensor. Even if you do get lucky and catch a leak with a sensor, that's not going to do anything to plumbing failures that occur elsewhere. I'm using the community integration for Flo and that works amazing too. I have picked up some accidental leaks and spills from my sensors and it reliably triggers the Flo everytime.
TIP: If you do decide to go with Flo, forget about the stupidly expensive Flo battery backup, and instead just plug it into an APC UPS.
For me, it's all Nest Protect (I have 8 of them). I integrate them to HE via Homebridge. Works perfectly and in my opinion, Nest are the best for multiple reasons. No other smoke detector can touch what they offer. Yes, it's Alphabet/Google and so I could be SOL on the features someday, but I think it's much less likely for that particular product than something like an oven. Time will tell, but so far (Since July 2015) they are fully supported.