Posted: 14/03/2014 at 11:06
Gary, I'd make your own. it's cheaper and you can control the quality. Buy MPC in bulk along with the sand and topsoil. Use a cement mixer to mix, then bag and use as needed.
Top dressing is easy to do, and having been a commercial gardener, control over cost and quality, is better than trying to save a few quid, by buying in stuff.
Customers will appreciate the effort if it's explained to them properly and the results will be appreciated.