i guess its one of those things, its no more complicated than any other engine to remove, however someone who knows what they're doing (ie MRC or Unit20) is likely to do the job quicker with less chance of a **** up, and are likely to know of any quirks etc, but then you pay for this experience.
When you start getting into slightly dodgy outfits doing work cash in hand, things could get really bad. If they break things when removing it, inevitably it wont be their fault, and how sure can you be that the work is done properly and will actually last...