I have a couple, but only of the smallest size. I got them either as a promo/combo thing, with some purchase of who knows what product in a large gallon jug or something. I'm pretty sure both are from DD.
I haven't tried any sort of "serious" chemicals in them. I may appear to be the Master of the Obvious, but the dual action is nice for the chemicals with which you spray more copious amounts. For me, this is typically ONR (particularly as a clay lube if not also for other purposes), and medium strength APC.
But it's a double edged sword for me, since these bottles are of the smallest size, and that I use them with the products that get the most trigger pulls so to speak: I'm always refilling the damn things. However, I rather refill every once in a while, than to have to double the number of trigger pulls. I think of when I use APC at a rapid fire rate, and how I would sometimes switch between left and right hands when using any other bottle.
Nutshell: If "want" becomes "need" one day for you, I would only advise trying a larger size, of which I've never tried. IOW, I think I would rather have one big one than two small ones, but I also say that without remembering their respective prices.