ZWAVE Plus repeater necessary?

FLiRS allows battery devices to be (reasonably) responsive. Most (ie nearly all) ZWave battery devices sleep for 99%+ of the time - you can’t send them anything in that period. This is fine for sensors, but if you want to open your door, then you don’t want to wait 1 hour till the lock wakes up.

A FLiRS device will wake up more often (a number of times per second - depending on the exact implementation). This makes it pretty responsive - a bit of lag, but less than 1 second, and certainly not 1 hour.

Any battery device can use this system, but at the moment, it is mostly implemented by door locks (ie something that opens your front door). There are a couple of radiator thermostats on the market now that also use FLiRS which is great for them as well).

You’ll need more than this for a good mesh. It’s pretty hard to give exact statements as the performance of RF, especially with these devices (small antennas that aren’t aligned), and different types of house construction (wood, brick, concrete) all impact on the performance.