I am a great believer in belt and braces and a bit of string.
I have the PGPS database loaded on the MIB2 (the piece of string as it does not give loud enough or earlier enough warnings), a separate Cheetah GPS camera detector with audible warning set at 80mph and a Snooper4ZeroElitePlus GPS, Laser and Radar detector with warning set at 60mph.
Each dedicated detector uses a different database and both have lifetime updates included in the purchase price. The Snooper is supposed to have detection up to 1 mile for Radar and Laser – apparently it is supposed to pick up Laser scatter from when the gun is used to check cars in front of you – I do not know if it works as described as I have yet to come across a working Laser based site, I know of several local such sites but they have never been in use when I have passed them by.
This is not because I am a dedicated speeder but as others have said attention can wander at times especially if you are concentrating on the road and not the speedo and if you are on a road less travelled it can be easy to miss a speed sign, especially in summer in the country when hedge growth obscures the signs – there are several sign I know round here that are currently totally obscured – and I prefer country routes to main roads.