They all do the same job. What features do you think you need ?

The only possible benefits from one over another is visual appeal of the gauge. Connectivity with other devices, say if using Innovate products to log multiple items, obviously Innovate makes more sense as Stack or AEM wont be compatible.

The MTX has two programmable 0-5v analogue outputs, not sure what the others offer.

Doubt any of them have alarms, as without more inputs any alarms would be pointless.