Note, the following comments are based on what I see in the picture shown, I don't have any additional info on this unit.
miker: Looks cool. Can't wait to see some more pics. 300L/hr is fine unless you have a massive need for flow. .5m head is plenty for me in a midtower case. Curious how many W they say it will dissipate with no fan and all...
I agree, it looks like very high bling-bling factor, but I have very high doubts about whether it would work well or not...
300LPH translates to 5LPM or about 1.5 GPM with NO FLOW RESISTANCE! 0.5M head is about 19" of resistance after which you have NO FLOW! (For those more familiar with fans, the flow rating is equivalent to the free air rating and the head pressure is equivalent to the static pressure) This tells me that the pump is severely lacking in power, and will not pump a meaningful volume if there is any flow resistance to speak of in the rest of the circuit. Note that in a closed loop system, 'head' height doesn't make much difference, the water flowing down hill generates enough suction to help keep the water flowing uphill, even if the peak height is greater than the nominal 'head' rating. What the head number DOES tell you is how much flow resistance the pump can handle.
As a comparison, The three most popular Eheim pumps have GPM ratings of 2.6 for the 1048, 5.2 for the 1250, and 10.0 for the 1260 / 1060 (I've seen both model numbers, not sure what the difference is) the 1250 has a head rating of 6'7" or about 2M, I'm not sure of the others but believe they are about the same, or better. My Iwaki MD20RT will pump 8.0GPM (30LPM), with a head of 14'6" or a bit over 3M.
The only saving grace is that a given amount of flow restriction will make less of a dent in the flow volume as the flow amount drops. Thus a flow restriction that would bring my Iwaki to it's knees won't make much difference to this Zalman pump - If the flow is lousy to begin with, it is hard to make it worse....
The way the pump appears to be part of the base, I suspect it would also be difficult to swap the supplied pump out for a better one.
The thing is also made from aluminum. This means that unless one wants to deal with corrosion issues, it will be necessary to have all the rest of the metals in the system be AL as well, which will have a minor negative impact on efficiency.
Next is the convection cooling idea - It might work, the tower appears to be heavily finned, and it's big enough that it might make a very good radiator. It appears that both the coolant supply and return lines go into the base. Presumably the pump inlet suckes from the res, the supply line is hooked up to the pump outlet, and the return line just passes through and returns to the res. What isn't clear is how they prevent hot return water (which with such a low flow rate I would expect to be VERY hot) from mixing with the cooled supply water. I see what look like inlets and outlets in the top of the base unit, but nothing in the tower tube that would keep them seperated. (but that could just be from the photo angle...)
Overall, if I was to predict results, I would expect that it would work, but not as well as a higher flow, all copper system. I expect that it would be able to handle ONE CPU, but not additional loads like Duallies, GPU's, or hard drives. Not needing a fan would make it a quiet item (Unless the pump is noisy), but depending on the system you might still need fans in the case for all the heat loads that the tower couldn't handle.