I have used SEEMIS products on a very in depth level as I used to be a developer.
The SEEMIS products are taking over Scotlands schools because of a few reasons.
Firstly there's a lack of competition. Pheonix are the only real other choice and while their products are cleaner, tidier, faster and better looking, Click+Go (the SEEMIS product) has a two week development turnover so it's entirely possible that within a week or two of a school suggesting a new feature that it'll be on the way to being developed. The helpdesk for SEEMIS is linked almost directly to the programmers who work on helpdesk all week in turns with a target to clear the helpdesk before the end of a working day so the support is great.
Secondly, Click+Go is government funded so, for schools, it's pretty darn cheap.
Thirdly, all SEEMIS software is aimed at education in Scotland only so you get a very customized product.
There's no way Pheonix can compete.
Click+Go does have it's problems though. There are no design documents and no design phase in old or new additions to the product and this slows production down a little which is then sped up again by having no real testing phase. So what you get is a pretty fast service that is very likely to suffer from bugs from it's early stages throughout it's lifecycle as it's continually patched.
There's also very little thought put into the HCI and as a result it can be very ugly on some sreens and every screen looks different.
All in all it's a great product but it's ugly, clunky and can be very buggy but there's a great helpdesk to make up for it
Hope this helps.