Yep, definately buy it. After all for £85 what can you get in the air nowadays? you'd be lucky to get more than two possibly three practice entries/holds.
If you're new to instrument work or going for your IMC then you'll probably find that the first couple of instrument flights you do your brain will get somewhat overloaded! I bought rant mid-way through my IMC lessons and now wished I'd bought it before I started.
Just remember it will save you time, money and improve your instrument flying in the long run...