I had the chance to try Chirp, simplex on a couple of PMR446 radios with Julie this evening. We still didn't manage to exchange Chirps on air. Having tried the test simplex, that's eliminated the audio circuitry of the repeater from the first test. My guess is that we're not getting the audio bandwidth we need.
However, the lovely people from the Chirp team have been in touch, so we'll see what we can come up. It would be exciting to get something working.