We have a 25 gallon Barker (4 wheel) tote tank. Have had it for a very long time, about 10 years. Its worked really good for us over the years. Really like the 4 wheel kind, that you tow to the dump station. Makes it very easy to use when you only have to 'pull' it, not lift it when full. Wouldnt want to lift one end of that thing up when its full!
Yes, we use ours pretty regularly, as there are a few places we camp regularly that don't have sewer hookups, but have a dump station close by. And, we can fill up the grey tank in just 1 or 2 days of camping (showers fill it up quickly). We probably use it 2 or 3 times a year.
Yes, the wheels the Barker tanks (used to) come with, are pitiful. I did the upgrade to the wheels/axles, replace all 4 wheels with real, air-inflated tires/wheels. That was a HUGE improvement.
Not long after I and a few others on here did that (wheel upgrade) and talked on here about how we did it, Barker announced their new models that had those wheels/tires from the factory. And, they did it almost exactly how we had. Haha, don't tell me manufacturers don't read these forums and learn from us how to improve their products. :)
Only real issue I've had with it over the years, is a small crack in the case right where the dump valve is. I've sealed it a few times with JB weld, but it keeps re-springing that leak every so often. Its only a drip, and we only ever use it for grey water, so I've chosen to pretty much live with it.
As some have already said, you definitely have to think about the places you'll camp, how you'll camp, etc., before buying one of these. For a lot of people, they wouldnt be very useful. I like the idea some talk about, about putting the tank up on a pickup bed or something and pumping the water into it. That'd make it even easier to use.
Need to think about storage, too, as these things can get huge depending on what size you get. The 25 gallon tank we have, just barely fits in the trunk of our towed vehicle we bring (Ford Fusion). Any bigger, and we'd have an issue. Thats part of why we went with 25 gallon. On both the last RV we had (TT) and the present one (Motorhome), the 25 gallon tank just fit where we wanted it, and going any bigger would force me to store it somewhere else where I didn't want to put it.