Yeah, its really for stuff not going into the food chain directly - animal feed is fine. Cheep as chips; the stuff is free but you pay for spreading. I think it works out about a grand for 150 acres and put about 8t an acre on. That gives about 40kg of slow release N each year for 2 years, and about 110kg P for year one and about 60kg P year 2. And loads of bulky fibre for worms and soil strucutre.
For heavy land would suggest putting on after barley or rape. You can have it put onto cultivated land, subsoil out the wheelings, and run a KKK over it, or wait until it is spread and then go as normal. Dont see the point of ploughing it in on heavy land, and 8t an acre is not a lot of muck to mix in.
Advantages are you get two years worth of phosphate for about £6 or £7 an acre. No potash in it. Also get your soils tested as part of the deal.
Thats the traditional stuff. There are downers - big wagons want to deliver in the wet. No control on when it is spread. More paperwork for safe sludge matrix. Less friendly neighbours. Less outlets for your product in theory. You get a big pile of what is essentially human turds next to your farm, possibly for 6 or more months. As far as I know, it is also limed for disease control, so you dont want to be getting it on you. Smell vanishes about a week or two after you have worked it in.
Here is some bumf: http://www.nutri-bio.co.uk/pdf/Nutri_news_km6Jun.pdf this seems to suggest that you can stick it (or at least the bagged stuff) on potato land providing you leave a big harvest gap. For most winter combinables, there will be a gap of upto a year for wheat following rape. There is also info about the granules which are more pricey. They are for you lot down south.