Yep, I've used it for almost 2 years now and I abused the heck out of it, except never let it stand outside in freezing temperatures
I think, more than anything, the lack of positive reviews is due to the fact that the vacuum is expensive (around $400), there is a general disregard for Oase since their items tend to sell for more of the "higher end" customer, and, when anything goes wrong, then it is all hell to pay and written in a review. There are genuine folk out there that have honest problems, but I have not yet experienced them and I have met very few individuals with the problems.
Pandovac4 is a strong pond vacuum but the flow rate is not so high that it performs a huge water change. The problem with some of the DIY vacuums that use waste pumps, swimming pool or hot tub pumps, or transfer or waste pumps is that the flow rate is quite high and this high flow rate leads to an unnecessary high potential water change. On the Pondovac4, there is a notch at the suction tool's handle and opening this notch allows you to control the suction power. When notch is all the way closed, I can pick up small 2" rocks.
Pandovac4 can be tricky to operate. If it gets "tired", then raise the suction tool out of the water to let it suck some air and this will trigger the lines to flushed and a container to be emptied. Then, continue vacuuming, not a big deal. If the motor is making some odd noises, then turn it off and then back on and let it suck some air again.
There is a special string algae attachment that comes with the Pondovac4. This causes the string algae to feed into the vacuum as a noodle instead of as a clump, but vacuuming string algae, stems, long grass blades, and huge clumps of leaves can cause the plastic flap inside the vacuum to stick open and this prevents the canisters from properly emptying. So, take it easy. Just don't go into a big pile of algae, leaves, etc, and take it in all at once. Just creep into it.
My pond is only 14" deep and about 10~12 feet wide, depending where I stand, but I am lazy for not wanting to walk around it. So, sometimes I put the 3rd extension on it and the suction does noticeably decrease for me after each extension is connected. I think much of this suction loss is due to the suction pipe being around 1" wide since, when I reduce the suction pipe with some PVC reducers and reduced the end of the pipe to 1/2", then the suction noticeably increases. I made a straight crevice and an angle crevice tool out of PVC connectors that I then tension slipped on the pipe (not gluing them).
I don't think the Pondovac line is made for crazy big ponds, such as those that are 10 foot deep, and, after I used mine, I would be interested in seeing the Pondovac cleaning up a 8 foot deep swimming pool, which I am guessing would be a little slow.
For the price, I think it's not bad considering that all the other DIY vacuums either take multiple steps to suck stuff out or are quite slow or are noticeably more expensive. Again, I know folk have had problems with the Pondovac 4 that forced them to stop using it, but I have never encountered those problems. Guess I'm just lucky like that... with this pond vac.
If you don't like the water waste, then you can simply put the vacuum on a stool or something then let it drain into a container. Let the debris and particulates settle and then suck the top clean water back into the pond.
Vacuum's waste outlet can't be raise much higher than the vacuum without it eventually clogging so the vacuum must always be higher than where the waste hose sits. This is due to the fact the waste outlet is gravity flowed out and not pushed by the motor.