That’s not something we can define here, unless you gave him a tool that he would base his new tool on, if he developed the tool himself, faster or slower is relative.Because I want something faster and better.
Please show me where you asked for a specific speed before he started developing the tool and where you provided a sample tool so he would be able to imitate or improve it.
Also keep in mind, some developers work different from others. Claiming it’s slow, or bad, or not what you expected is not a proper reason to avoid paying. As long as he provided a working product based on your initial description, he should be paid. Now, if you think his tool is bad, not working as expected, or just slower than free tools, then we can determine a better price for the tool that is more accurate to what he’s providing. But you can’t simply claim it’s “not what you wanted” just because it’s slower than you expected it to be.