Thanks much for the input Rosemary - I'll go check out.
I've also just discovered that Stihl offer a manual-pump back-pack sprayer and I am dumb-founded at finding a Stihl product that is, for once, competively priced (assuming it does offer pro-level reliability)!!
So another couple of sprayers to look at.
[Edit: price for Stihl 12 ltr sprayer might be competitive, but I was just looking at accessories - as usual, silly prices, e.g. a telescopic spray lance would cost almost as much as the base sprayer unit. So once again, Stihl = steal.]