For now I am quite satisfied, it's the second year I own it and I am quite happy. The only negative is the spray nozzle it has, which for olive trees like mine is not very convenient and you can't easily find a replacement because it has a different thread, so you need to improvise if you want to use something else. Generally, as a product it seems durable and the battery is more than enough; so far I have sprayed up to 13 tanks and the battery was still going, we're talking about 260 liters of material which is enough for 150 trees. For olives, which is what I want, you save quite a bit on material-chemical because you need about 1.5-2 liters per tree, and you can put in each field exactly what it needs in the quantity it needs without having 500-1000 kilos of material in the car that you have to use up quickly and is all the same.

I bought the double one thinking that if it breaks down or the battery runs out, I can continue my work manually in the field. In the end, you get tired and stop more easily than the machine does. So buy the single one, only with the battery, and I think it is more than enough, at least the way I work. It looks very high quality as a material on the outside, although all the internal components are more or less the same everywhere from China. It was used for almost a year in 14-acre kiwi fields and everything still seems to work properly. The manual pump has also been removed and the weight dropped to 4.6kg empty. I don't know, maybe I would buy it again, although my first thought would be a 16-liter lithium one for less weight. Not that you save much...800g.
Edit: In the 2nd year the pump started to have a small leak resulting in not reaching the required pressure to stop working.. For now, it is used like this until it is replaced. Cost 15-20€
Edit 2: It was about to be used for the third year but it completely stopped spraying. Now what is wrong, only God knows. The battery works.
Anyway, in the end, it was a bad choice. You don't even need 20 liters because it becomes excessively heavy and impractical, nor a double manual/battery one. Compared to a Cresman I bought with a lithium battery, the difference in usability is huge. I just hope it lasts two or three years because it is not for more than that

It is quite heavy due to the Lead-Acid battery.
The first charge lasted about 20 hours. The next one, after about 3 hours of use, lasted 5 hours. Overall, the battery seems to be more than enough for a day's work, but it takes a long time to charge (you have to put it on charge at night to be ready the next day). It is very powerful in terms of pressure. There is a speed regulator for the pump (I usually use it at a low setting and the quantity is sufficient for one nozzle). I bought another nozzle because the one that came with it didn't suit me (+a new connecting hose to the sprayer with a total cost of €7 from a local store). The common nozzles for manual backpack sprayers do not fit because the connections have different diameters. The straps for the backpack are not of very good quality and they get tiring during prolonged use, especially if you fill it with 20 liters. There is a soft cover integrated into the sprayer for back/waist protection, and it is very helpful. If it had a lithium battery and the right nozzle, I would give it 5 stars.

Very powerful sprayer. In terms of build quality, it's not Chinese but not perfect either. For its price, it's great.