I've got a Black Spire "Big Ring protector"from Chain Reaction.
Apart from the dodgy name

it works well, but is quite a lump even with the C2 plastic version.
I put it on for the alps then took it off to save a bit of weight. Since then, I have lost most of the teeth on the big ring, mainly while riding McMoab at Kiroughtree! I'm going to replace the big ring with a regular bash ring next I think.
What I have found though is that I can clip pedals/rings while climbing (e.g. whytes level at afan) but flipping the pro pedal on really helps stop this by keeping the BB high.