I recently read a few articles on these hydro systems by Corasir and Antec. None talked about the pump, none really provided trustworthy fan noise assessment, but all these reviews agreed on one thing - these systems are overpriced and cool just "well", at best. But they're really just overpriced gadgets. Easily surpassed by most Thermalrights, Noctuas, Scythes and the like, in terms of cooling efficiency and noise. Sure, you can replace their stock fans, thereby adding cost, but that won't make these systems much better coolers. Just my 2 c.
It's not an obvious alternative to the usual tower coolers you mention. If I needed a good cooler for a regular tower case I'd go for Thermalright.
These water cooling systems are superior in some situations though, like when there's not enough room for a decent heatsink, ie in many small cases.
In terms of space needed above the CPU, these water cooling systems competes with Scythe Kozuti and similar low profile models.
Sure, the price isn't the same, but it's simply the best you can get in some situations.
I wouldn't call them overpriced, they used to cost a bit too much, but since Antec launched their models the prices are lower.
The 620 cost €46, while HR-02 cost €50 and Venomous X-Black is €49. Just comparing the price here, not performance or noise.