As others have noted, this reservoir does have a tendency to emit bubbles continuously through the outlet, which can't be great for your pumps. But I did find a good solution: mosquito netting.

I just shoved a two-foot-long strip of mosquito netting into each chamber. This traps air, and even traps sediment and particles that would otherwise foul the system. It doesn't look great, but does the job amazingly well.

My suggestion for EK: redesign this waterblock with a much deeper chamber, and perhaps even some baffling to increase the flow path length. (Posted on 6/28/12)

Note: This holds less volume of water than the single EK-Bay Spin. So if your individual loops need a certain amount of water then make note of this.

The Reservoir itself it very well constructed. It fits perfectly into the drive bays and the screw holes line up perfectly to my NZXT Phantom case. The seals are good as it does not leak. At least not yet. Knock on wood and cross fingers. Don't want to jinx myself. :)
The look of the Reservoir is nice. When you add the LED's to them it illuminates nicely. Also if you have UV fluid in your loop yo can use UV LED's to help light it up in the Reservoir. The Flow Indicators are a nice feature to have. Not only do they add to the look but they do help in telling how well your water is flowing. Also it comes with two separate colors. A red and Blue, but there are two other colors in the market that I have seen. (Yellow and White) Who knows you may be able to find other colors to match your setup.

Now a few things I should point out:
First thing is filling it. You may want to leave some slack in your setup in order to slide the Reservoir forward to fill it. that is if you do not have enough drive bay slot open above it. I use a funnel with an extra piece of tubing to snake into the holes.
Also depending on your setup you may get a lot of bubbles. This can be remedied though.
One way is to slow down your Flow Speed. This will keep the water from splashing down to hard and lessen the amount of bubbles made.
Another way is to keep as much water in the loop as possible. If the Reservoir itself is full then there will be very little bubbles. The waterfall effect is a nice touch but it does cause bubbles in the water.
Another way is to add a second Reservoir to your your loop. This may seem like an odd thing to do but its not. For one you add more water to the loop, which some loops needs. Second it gives the bubbles another place to collect and disparate. I myself have done this. I used my EX-Multioption X2 RES 150 that I got with my initial kit and added it behind the one loop for my CPU. That loop actually has hardly any bubbles at all running through it and lowered the temps a bit which helps since it is using a single fan Rad. Less water the easier for it to heat up all the water. I think I'll be buying another Reservoir for the second loop as well. It does add to the look on the inside of the case. So now I have a nice look at the drive bays as well as inside. :)

All in all it is a great Reservoir to have. It will add a unique looks to your rig and when setup right will function well. I would suggest this reservoir to others. Its is a good product.

A few things I will suggest to improve it.
Add more volume. The Drive Bays are pretty deep so you can go back with it a lot more. This may also give the bubbles more of a chance to collect in the top of the Reservoir when you are trying for the waterfall effect.
In regards to the bubbles. Maybe add a partition from where they form to where the water leaves the Reservoir. If the Reservoir was large like I suggest this could be possible.
What would also be neat is a accessory to help with filling the Reservoir. A device that could use the drive bay slot directly above it which could open or slide out in order to be used as a place to fill from. (Posted on 2/5/12)