Hello!
That is all true, according to what I was told by my PB and the literature I have read on the liquid solar covers. However, I have a heat pump (electric, so not as 'quick' as Natural Gas to bring temp. up), and I tried the liquid cover for our first season. My PB told me that you could go disrupt the water and see evaporation come off of it, proving that the cover worked...I guess that was true to some extent, but I still saw evaporation on cool mornings, even if the water was still.
When we got a solar cover, the difference was immediately noticeable. You don't have much to lose if you try the liquid solar cover, so you may want to give it a shot. But IMHO, the bubble-type solar cover wins hands down.
And I think the bubble solar cover is definitely marketed as a device that will stop evaporation and not necessarily warm up the water, but I kept it on for several days at a time at the beginning of this season, and with the heat pump running my water temp. rose WAY faster than it would have with just the heat pump and no cover...so I'm not sure exactly how that all worked out technically speaking, but it seemed to really help.