I You need to v nail a frame first to stabilize it for cross clamping. I've yet to see a v nailed frame that cross clamping couldn't make pretty near perfect. V nailing plus cross clamping where necessary is vastly superior to working with 4 Master Clamps; we never considered using the Master Clamp in production.
If you have a v nailer, K Body type clamps would be vastly better because they allow way more force than the Master Clamp and are way more adjustable as the picture on our web sight should show.
Are Master Clamps worth the expense?
Stanley used to do some neat little strap clamps. Just a pressed steel body with a ratchet mechanism with a length of webbing. I have about 10 of them. Used them for years and they are very useful when assembling big frames single-handed. They don't have corner bits, but a bit of card does the job if you need to cushion the corners. But they work really well on scoop-back mouldings as the webbing moulds itself into the scoop. You can get really high pressure on because you can cinch up the ratchet with a wrench.
As well as framing they make very good general woodworking clamps, especially on irregular-shaped things like chairs and wotnot.
Pity they don't seem to make them anymore.