I’ve never been much impressed by the results from my breadmaker (a Panasonic SD253): the bread was usually OK, but not good enough to prompt me to use it regularly. I think the automation by the machine of the breadmaking processes is not going to give anywhere near as good a result as those that can be achieved by making the bread by hand with good technique (technique not just being the physical activity of kneading, but all the other factors which influence the results, e.g. timings for the prove/rise, correct oven temperature etc., i.e. skill based on knowledge and experience/practice).
Looking at the comments on Shipton Mill’s website recepie for GF flour, getting the technique right appears to be even more critical for GF flour, and it looks unlikely that a breadmaker would deliver satisfactory results.
Before spending money on a bread machine, I would spend £30 on a 16kg sack of Shipton Mill’s GF flour and have a go at making loaves by hand. It might take multiple attempts and failures to get it right, but the results will almost certainly be better than with a bread machine, and you will be better able then to decide whether the results justify carrying on baking by hand, or whether to buy one of the GF breads mentioned above.