Tank is very hard to detatch.
592834
Overly complicated base is hard to remove when I need to refill the tank.  It locks in place and is very difficult to get unlocked.  I can't even tell which way I'm supposed to rotate it in order to match up the locking tabs to the opening.  This is replacing my old tank that just popped out for refilling.
2231042
Good product, but the fish seem to bite and pick it off the coconut husk which has the Moss tied on with fishing line. So once it all gets picked off its almost impossible to get attached again.
654901
The thing is just designed really weird. The red button shoots the cannon rather than draining the tank. The green button under the cannon releases the tank but gets stuck really easily. You'd think that when the water drains from the tank the spinner would spin; but it doesn't. The drain is positioned back behind it, so no water actually flows onto it.

The suction cups worked really well, and my kids enjoyed it for a few months, but now it has mildew growing on it (i know i could use bleach or vinegar on it) but the green button is perma-stuck. Overall, it was cute, and I don't regret buying it, but I do think that the design was really bizarre.
4603310
It's a really good case, but taking it off is close to impossible. I was trying to get it off for a good 15 minutes before I decided to give up.
2639239
Overall I really like this product. However, every couple of days I have to reach in my aquarium and resecure it to the side of the tank or I will come home and find it sitting at the bottom.  Needs to have a better way to secure it to the tank.
3196281
This thing is not quite. It has a constant hum from the motor sucking the water into the reservoir. Once you dismantle it to clean you will notice that the parts are very cheaply made and do not interlock easily when you attempt to put it back together. The flow resistance lever is the biggest pain to reattach, I just leave it off. Other than that it does exactly what it advertises.
129423
Hard to remove the tank, and usually the water spills over. Everything else is very good.
2800611
First things first when installing this my roommate broke the plastic tubes that hold the dock in place so I had to tape it together.  The suction cups are hard to get on which led to breaking the tubes.  Once installed it worked alright but my turtle outgrew it after a year or so.  Time for a new one but I'll need to get a bigger tank first to fit the larger one.
2401522
It took a while to figure out how to get it going, but once I figured it out, it works fairly well. I don't think I was able to get everything that had settled down to the bottom of the tank. While I was trying to use it, I ended up stirring up the tank so everything got re-suspended in the water and had to wait for them to settle down again to vacuum them up.
4322645
Simple. I had to isolate a aggressive fish out of my tank. Buying another tank was out of the question. This was a great solution!! I bought t he large size. It happy holds my Red Tail Tetra.
3032210
We have two cats.  One kept it on , the other managed to lose it.  The safety disconnect is a double edged sword it would seem.
1566140
The hooks, while very secure, are difficult to remove in my vehicle (BMW X5).  I have to struggle with it, and this takes time.  I cut the retaining guard off one of them, and it is much easier to detach.  Unfortunately, it gets tangled with the net easily when its not attached, however.
600505
We  purchased this to add a little additional warmth to our tokay gecko tank. It worked wonderfully, except was almost impossible to get all the air bubbles out. I have a lot of experience in applying films and removing bubbles, and this was very difficult to do given the thickness of the product. The heat transfer was decent enough even with several remaining bubbles, but our terrarium has extra-thick glass so this definitely wouldn't have been enough without the lamp above him as well. The tokay did especially like the side of the aquarium I stuck this to though, and would "hang out" on that glass side for days.
2108225
One of the screws is placed under the stem, making it very hard to reach with a drill or screwdriver for installation onto the tank.
2106192
At times hard to disengage , seems with tension on it it's harder to release , I would have to tighten to get it to release , finally had to cut off because it would not release , will not buy again !
940802
worked great but takes alot of strength to close. my mom cant hardly close the hatch by her self, she has to ask for help at the supermarket
4155552
It's a good hard cover that provides good protection but it's EXTREMELY difficult to get off if you want to change it. You'll break your fingernails trying to get this bad boy off.