I've carried one around for a few years but only had to use it a handful of times - more often than not I'll just tie a length soft rope (that I also carry) round the legs and sling it over a shoulder - but with a doe and a follower, I'll put the wee one in the yule and hang the doe on my shoulder. That way I can easily put her down when I need a rest! If I had very rough ground to cover and needed both hands free to hang on e.g. on a climb, I'd probably use the yule as well.
The yule is a good idea, but I had to reinforce much of the stitching between the sack/sheet and the shoulder straps on mine after it's first use (!) when it started to come apart! Since then no problems.
I carry it rolled up and strapped under a bum-bag (which carries my bit of rope, gralloching kit, first-aid bits and torch) - that way my shoulders are free and I can shoulder the rifle unobstructed. (If the yule is full - then yes I'll have straps on my shoulders - but then I'll think twice about shooting anything else, specially with one on my back!)
Anyone with a bit of patience (or an industrial strength sewing machine) would, I think, be able assemble their own; it is a brilliantly simple design, and does work!
Alasdair.
p.s. a bit of rope is more versatile than a purpose built roe carrying sling.