it will sail about 30 degrees each way if the wind is above 10 knots or so. Probably worse than the average sloop because the mainmast is so far forward. However setting even the double reefed mizzen (maybe 120 sq ft) and it is instantly rock steady into the wind. While sloops all around are dancing back and forth.

Having said that, I can tell that the boat does tack slightly by the sound from the mizzen. I think this is the reason you want the V shaped riding sail. My mizzen doesn't flog (it is a full battened square head sail) but it does invert with a "pop" every so often with wind shifts or the minute amount the boat does hunt. The V shaped two wing sail will not do that, both sides are full all the time, also there is more restoring force at smaller angles of deviation. I saw three sloops with this type of sail in Elizabeth Harbor in the Exumas this winter and watched them for awhile, it seemed to be doing a good job of keeping them straight compared to the boats around them, and no noise.

We almost never anchor without some of the mizzen up.