Hmm, I'd be interested in a chinrest recommendation for my viola. I currently use the Kaufmann chinrest that came with it; it's supposedly one of the lower chinrests on the market but I find that it still digs into my jawbone a little more than I'd like. (I'm also already using a low-mounted shoulder rest -- it's a Mach One, but with shorter legs borrowed from a Muco shoulder rest.)

I think chinrests do matter. I got a custom-made chinrest this summer, and it's made a huge difference. Unlike rucksacks, the longer you play, the easier it is to tell the difference. I've played as much as 8 hours in a day with with the new chinrest, with no discomfort, and it's made shifting and vibrato much easier.

Until February 2018, I used the Kaufman chinrest that came with my viola. It's already one of the lowest on the market, 17 mm high, and it was already too high. I could not fit the viola between my jaw and collarbone at all, so I had to rely entirely on my shoulder to hold the weight of my viola. It caused back pain when playing for long periods, but I thought I had no choice because I hadn't seen anything lower.

In February, I learned that violin and viola chinrests differ only in clamp length, and bought a Joachim violin chinrest (I attached it using the viola clamp I already had), which is only 12 mm high but flatter. That mostly solved the problem of being unable to rest my viola on my collarbone, but I found that it caused shoulder and neck strain because it was too flat and would slide out from under my jaw if I didn't either raise my shoulder or clamp down with my head. I ended up switching back to the Kaufman in April, because it caused fewer problems.

Finally, in late May, I attended a concert at a chamber music festival where I noticed a violist using an ultra-low chinrest. I asked her about it at the end of the concert. She told me it was a custom-made chinrest by Frisch & Denig, and that it actually wasn't super expensive. It took me longer than most people to get a fitting scheduled, because most of the people who do fittings have only the kit for long necks and the nearest person with the short-neck fitting kit was in San Francisco, but I had my custom chinrest by mid-July. I had to pay separately for a fitting session (the fitters are mostly teachers and luthiers, not F&D employees, and charge for their time) so the total cost to me, including both the fitting session and the actual chinrest, was about $180. The cost is likely to be lower for most people. I used my new chinrest at a chamber music workshop in late July where I played viola for about 37 hours in six days without discomfort. 

As for the chinrest itself, it's a modified Brandt chinrest, ultra-low with a pronounced lip in only one corner. (Frisch & Denig chinrests are based on existing chinrest patterns, with height and horizontal position adjusted to fit.) My chinrest is 10 mm high at the bottom of the cup, and modified to allow it to be placed much closer to the tailpiece than is typical for side-mounted chinrests. I can't use a center-mounted chinrest because I need it to be lower than the tailpiece, so the custom chinrest got me as close as possible. One huge benefit: my viola stays in place at a comfortable angle when I'm facing straight ahead, which greatly reduces neck strain.

I think custom chinrests are an option worth trying if off-the-shelf chinrests are not working. Also, a one-time expense might be better than spending a lot of money constantly changing from one chinrest to another. I'm told that most F&D customers are people with long necks who need extra-high chinrests.