I wanted a sat nav which was as detailed for continental European roads as for UK roads and which could be regularly updated. This filled the bill at a reasonable price. However my criticisms are as follows:
There are quarterly updates which you download by internet. However you cannot just download the update for specific countries and keep the "old" map for those countries you are less interested in. Those you fail to download get deleted from your sat nav system. This means that you either accept that your sat nav will have missing countries or you have to download the files for every single country at the same time - you cannot download different countries at different times without having those already on your system deleted. As each file is pretty large, and the complete set enormous, this is a real pain in terms of download time - many hours!
You can choose different types of vehicle profile e.g. car, lorry, motorbike, etc. - for most users the car profile will be the one to choose. However this can direct you down some very narrow, badly maintained country lanes if this is considered the "quickest" or "shortest" route. Unfortunately you never know this until you start down the track, nor do you know quite how long the track is before it becomes a normal road.
In terms of routes, the system tends to underestimate the time it will take to reach of destination. Other systems I have used tend to over-estimate, and I think I prefer an over-estimate.
Like all sat nav systems, some of the recommended routes seem pretty odd. In particular the system greatly under-estimates the time it takes using routes which pass through central London.
The destinations shown on the maps are excellent and very detailed but not all can be found using the search facility. You sometimes have to input the name of a place nearby - it is only when you zoom in on the map that you find the precise place you are looking for. I suspect that using a post code is in fact better than using a place name.
The screen size is adequate but I have used built-in sat navs supplied with various makes of car and these provide a much bigger and better screen. Unfortunately they cost typically four times as much to buy.