Hi Martin
If you have the option of taking on the staff to your payroll after 13 weeks without paying a salary commission to the agency, then (in my experience anyway), you're being offered a very good deal.
My personal belief is that agencies tend to offer staff much more on the basis of availability than ability, and I'd confidently say that I've been entirely happy with around 30% of the agency staff I've employed.
I think the efficiency of agency staff is very strongly dependent on the amount of supervision that you're able to commit to them, and if you have the resources available to offer this then you're likely to get value for your money.
Incidentally, I sincerely hope that I didn't offend you in offering an alternative viewpoint to your post. Since starting my cleaning business last year, the range of opinions and expertise, including your own, that I've drawn on using this message board have been invaluable, and I don't think peterdirectors issue, like so many others, has one right and one wrong answer.
Callum