pscan.eu was originally developed to give a DIY diagnostic tool to owners of 1990's Rovers which OBD2 code readers and diagnostic tools won't communicate with, but it will also do a lot with the MG Rover era cars too. There are one or two members of the forum who have one and speak highly of them. I expect Talkingcars will come in and give you a more informed view of it.
Of the two manuals, the Haynes is a fairly straightforward DIY mechanics manual which covers most of the things you are likely to want to do.
The other manual is a single volume copy of the genuine Rover Group workshop manuals for the cars, and also covers the engines and the gearboxes in detail (apart from the 2003-on IB5) and is very comprehensive, if a little expensive. A hunt around should find you one significantly cheaper than the one you have linked to (I have seen them available for a little more than £30).