In the days of mITX or MATX systems, 2 radiators will be hard to stuff into those small cases.
If a case can be part of the upgrade, there are plenty of options, even with smaller cases, and many will have enough room as-is, if they did not go with slim desktop form factor small cases. I will likely not bother going with water, but my case, which I chose for air cooling capability and aesthetics, can fit a 240mm in the front, and 120mm in the rear, with just a little work to space out the front one a few mm (there's a rivet in the way), and that would still leave ample room for my CPU's HR-02 to stay in place, so long as it shared a fan with the 120mm radiator (depending on GPU block backplate depth, anyway). With water for CPU and GPU, the case's confines would seem cavernous!
Mini-ITX and MicroATX add some wrinkles, but are nowhere close to being show-stoppers, even with multiple separate radiators. That said, without overclocking, a single thin 120mm would handle most midrange computers. Overclockers tend to want to keep the water's temperature delta low, like 5C to 10C, while many of us might wonder what the fuss was about at 30C
A relevant question is whether the product makes sense from a cost point of view. The lowest priced AIO coolers start at around $50~60 before taxes or shipping. Add the $30 for the G10, and we're at $80~90. Such a setup would probably be better than a similarly priced air-only cooler for VGA cooling as well as overall case cooling (because of the water cooling system's ability to move the heat to the perimeter of the case where it can be efficiently evacuated). But it is more complex, and because of the pump, always likely to be a bit more audible even if the fans can be turned way down.
I have looked at water cooling just my GPU. With a suitable pump (DDC, as recommended occasionally here), no dedicated reservoir, and buying all new parts, made for use in PCs, $200 is about the lowest I could pull it off, and even that's pushing it. As a first-timer, it would probably be $250, by the time I dealt with unforeseen installation issues. I'm a bit leery of AIOs/CLCs, myself, but however much sense it may or may not make for noise (given pump noise), I think it does make sense for the cost. The design looks suitable for use with large CPU coolers, as well, that some good air video card coolers may get in the way of (Prolimatech's MK-26 backplate, springs, and screws come to mind).