If I were in the market for one, I'd probably go for a Nereus system. However, I don't have an LPG sensor and have no intention of fitting one. If you turn the gas off at the cylinder when it's not being used, there's no risk.
Yes I like my Nereus system, would avoid Pilot. Nereus is better designed for easier installation. Looks neater. And the sensors don’t break as soon as they get wet.
+1 for Nereus. I installed a twin detector CO/LPG last winter, and it was simple. The LPG detector is water resistant, and is mounted low down in the bilge in front of the cooker, and the CO about 8 " from the deckhead a little away from the burners. Quality product and easy to install. Not cheap, but what price personal safety?
I favour the NASA as it has comparatively low current consumption (30mA cf. Nereus 60mA) and is a reasonable price (£67.60 at Seamark Nunn cf. £258 from the manufacturer).