With a 50/34 compact, a 12-30 cassette will have more chain wrap than a standard Shimano rear derailleur can handle. Even a 12-27 is over Shimanos wrap spec, but it works. The 3 extra teeth of wrap from a 30t cog will be too much.

Some people will say that you can make it work by setting the chain so short that it can't go over the big ring/large cog combo. I think that setting a bike up that way is a mistake. All it takes is one brain-fogged mis shift to end your ride and possibly damage your frame.

Get a road triple derailleur. That'll work fine and be safe.