I have one in my arsenal that I use once in a while when I am not allowed to spray. Then I found one in a garage sale for little of nothing.
The thing really works pretty good for a wagner product.
The button is appropriately placed so you can call for more paint as you need it. The flow is very manageable and workable. It will pull about any viscosity of paint, no diluting needed like the wagner sprayer, which I would not advise getting. You can work out of a one gallon pail or a fiver. The hose works nicely and is long enough to cover the entire room with the unit sitting in the middle.
Downside: It takes forever to clean the unit out. The job needs to be large enough to warrant using it because you will spend 30 minutes cleaning the unit out or until you see clear water. So, don't crank it up for only one room. Then, the roller knap needs to be thicker. I recommend that you buy another roller with thicker knap. You have to buy special rollers as these have many small holes in the core for the flow. Then, do not, I repeat do not apply too much pressure to the goose neck end of the unit by the roller. This will bend so easly and break. I actually wish that they had made a reinforcement bracket or brace in that area. You will see what I mean when you visually inspect the unit where the pipe takes a 90 degree bend to line up with the roller. To much pressure and this will colaspe. I was glad that I found the garage sale unit as I replaced the goose neck on the old one.
The thing nice about this is that it does save on your back and the unproductive time that you spend dipping and rolling in the pan. I would definately advise on the small expense.