Not sure if this is a bug or intentional, but the Proto Shield can't shield bump.
All other shields work, including the only other 0-star shield (Iron Buckler).
Also, though I know that there's a set price for a certain star level, but it seems unusual that the Proto Shield costs the same amount as the Iron Buckler when the Iron Buckler is better in every way.
I found this some while ago. It's a fun novelty but it's hard to put to use. Thread
Personally I think it'd be better to have a bump on it as that would let newbies learn about the concept straight away and not be confused when their first shield can't do something others can't.
Well Three Rings probably just didn't put a bump function on the shield because they knew that they would create guilds, and then rank requirements would be to use full Proto gear, making the shield as crap as possible for maximum challenge during FSC solo runs.
Eh. Shield-bump-power-osity is a function of star level, which makes sense because shields are kind of boring and lame and players should at least have this one ability increase to look forward to, to feel and love. So imagine for a bit that you're a dev deciding on what the various levels should be at your customized wooden nautilus themed desk- the natural start would be 0, nothing, no shield bump at all and the maximum.. well, a healthy bout and you probably have an idea of that too.
All of the proto equipment is directly outclassed by other 0 star equipment.