I have the SITD foot for my Janome - it came along as part of the convertible 1/4" foot package - but I haven't had any luck with it as I think the walking foot is better at handling the sandwich.
I have found that SITD itself is not easy, period! It works best, imvho, when I have properly pressed the joined pieces, first setting them, then pressing them inside out, then pressing them right side out - it leaves just a tiny bit of fold of fabric covering the seam and the SITD stitches are covered up. If I had to 'make it fit' to get my sizing, there is sometimes just the seam and no 'ditch' left. That looks weak. But I tell myself I will wash the quilt and it will pucker up a bit and that will soften the line. I'm only on the 8th project so I have a very humble opinion.