The advantages of the DR2d are small size, low cost, and a nice functioning IR remote which overrides 'hold'.
Sound quality is good. For pocketable 4-channel it's great.
Downsides are the somewhat clunky 4-channel operation, some difficulty in figuring out what the equivalent input sensitivity level is if trying to match the levels of each pair, the mentioned lack of level adjustment while recording 4-channle on the line-input, and limited battery life.
IME, the R-44 is far more straight forward to run as a 4-channel recorder and what I use when I don't need 4 in a pocket. I use and value both.
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The only other similarly sized option I know of is the Sonosax MINIR82 which does 4 analog in, 2 with phantom, + 4 more digital for 8 total and is about the same size I think. Far, far bigger $ though.