I have some experience of a Grand Rapids system in an RV.
It works very well, however you do need their EIS system to interface to the engine sensors, this has its own B&W LCD screen and is designed to be used standalone. If you use their colour EFIS screens then this B&W LCD screen is a bit redundant, but you do need it as the rest of the box provides the engine monitor interface.
The aircraft I have been working on has 2 colour screens which work togther well and have a data channel linked to a GPS. This means that there is almost an infinite number of ways the system can be set up. I have found that its best to turn off most of the alarms as they repeat on each unit so 3 button pushes are required to cancel them. However this is a small critisism as the units allow you program just about everything. This ranges from what is shown on the displays to the colours of the different segments of the dials. You can also program the alarm levels.
Software upgrades are very easy and take a couple of minutes and are free as are the terrain maps, although these are not high resolution and are more useful for terrain avoidance.. You can save the screen setup to a memory stick and then its easy to revert to an old configuration if you make some changes and decide you don't like them.
In addition the units will record onto a memory stick so you can record all the engine parameters. This is useful if you are trying to diagnose an in flight problem. Just switch on record and look at it all later in the ground. You can also record fuel flows at different settings and airspeeds and work out best economy speeds etc later. If you are an engineer you will love this capability.
I don't have any experience with other manufacturers to compare with, but the Grand rapids system is easy to program and use and I have not found any gotchas.
It does use quite a bit of battery so I would suggest fitting an external power socket to the aircraft so you can put a charger on while you are sitting on the ground programming it all. You can spend an hour or so changing configuration.
ZA