If you are on a budget and have basic cleaning needs, UD500 might be the better option for you. As a cost-effective product, it provides economical cleaning but may require the use of a brush or sponge for heavy dirt.
On the other hand, UD540 offers stronger dirt removal capabilities and is a polished product that can clean regular dirt without the need for additional tools. However, for very stubborn grime, supplementary cleaning materials may still be required. While UD540 delivers better results, it comes at a slightly higher price.