Basics
Interphase cloak operates on principle of "phasing" cloaked object out of normal timespace continuum. Ships using it can pass throught solid objects; their ability to pass throught forcefields is unknown. It is possible that weapons fire would simply pass throught cloaked ship without interferance; that, however, is unconfirmed.
Undetectability level
Very high, as Romulan Warbird did not notice Enterprise-D passing throught rock few hundred meters away until it decloaked. For comparation, Enterprise' crewmen who got cloaked by accident involving Romulan Interphase cloak left residual traces and gave off chronitn fieldphenomena when passing throught walls. Also the fact that they did not fell throught floor is, to say at least, wierd.
Safety
Geordy: "Commander, we ran impulse engines throught the plasma conduits, but you might wanna watch the intercoolar levels. If they get too high, they will blow entire relay system."
It is implied that Pegasus's cloak blew plasma relay system, so ship decloaked while passing throught asteroid.
