Yes, it's a potential problem if the requirement is in the RFM. The company I used to work for (a major supplier of police aviation) banned its employees from using "Prist" at refuel time due to the alleged hazardous nature of the stuff.
I don't know if there is an alternative product (why isn't there - the need obviously exists?) but it's a concern that if there was an accident involving an engine stoppage or power reduction due to fuel icing, the aircraft manufacturer would understandably step back from liability; not sure what the insurance company would say but I think I could predict the answer.
Nigelh, the potential icing problem is in the low pressure airframe fuel system (filter blockage due to fuel waxing, or water ice crystals forming etc), not necessarily so much with the engine itself.
The types(s) I fly thankfully have oil warmed fuel filters so it doesn't affect our operation. It's surprising that all aircraft manufacturers haven't come up with a similar modification now that UK fuel manufacturers no longer supply the additive at source. Have you asked the manufacturer's advice? There might be a "cold weather mod kit" available.