Hmm - if I'm honest, I can't see why any Detailer would say to keep clear of a Gilmour
Of course, a pressure washer and foam lance is going to be the number one choice, but if that's not an option for whatever reason, the Gilmour in my opinion is an excellent alternative.
With regards to whether you'll be disappointed by it or not, I suppose really that all depends on what your expectations are
Personally, I love using the foam lance and we even clean our conservatory windows with it and whilst I rate the Gilmour very highly, I simply don't think we could do without our pressure washer and foam lance.
Hope that helps!
Taryn