I want to start by saying that I highly recommend the HD4050 battery powered backpack sprayer.
Out of the box, I was impressed by how sturdy and well made it felt. It came with various nozzles and was easy to assemble. The back padding is perfect, and the straps are light but once filled with 4 gallons, you will not feel much of the weight. I also like that the top cap is wide, comes with a filter, and is insulated to stop spills. The wand felt comfortable on my hand, and I like that it can lock for continuous spraying. I also like that the sprayer has a drain spout at the tank's bottom side if you need it instead of having to flip over your sprayer. It's a great idea to have a drain spout off to the side. I have not seen this feature on other sprayers. One of the best parts about the HD4050, is the bottom of the tank design. It is slightly slanted, so the liquid drains down into the catch reservoir before being sprayed out the wand, which enables the tank to drain out entirely, and you can spray everything in the tank, unlike most battery powered backpack sprayers that seem always to leave 4oz to 8oz in the tank. The HD4050 packs a punch of 60 to 80 PSI. You will feel its power and know it's fully capable of getting any job done.
So far, I have sprayed liquid fertilizer, humic acid, liquid aeration, and kelp with the sprayer, and it did exceptionally well. I was even able to mix some of the products with no problems.