It depends what you are wanting from the lambs. If it’s meat for your own freezer, and you don’t mind them taking a bit longer to grow and being a little less muscley, then fine. If it’s store lambs to sell, you will get a lot less for Heb x.
You will probably get some horned lambs, if that’s an issue for you? If you don’t usually castrate, might be better to as these will be slower growing plus might have horns.
Not sure if the offspring will all be black? Depending on whether you expect to keep any until shearing this might be an issue?
On the plus side, using a primitive tup on first timers is a good idea for gimmers, in my opinion. I always use a Shetland if I can. Small, active, hardy lambs, come out running, know where the milk bar is and are very persistent in getting onto it. You shouldn’t have any birthing issues (although don’t overfeed the ewes as horned ram lambs can have big heads with the horn buds), and by the time they’ve reared these, your girls will know their job for next time