Oscillating blades, they're expensive, it doesn't take them long to wear out.
When they're worn out, take your grinder and cut some new teeth on the blade. That's it. Then the blade will cut well again. As you see I made big triangle teeth. The little ones don't last long.
I use this tool all the time in woodworking to correct little mistakes. Oscillating tools are not a replacement really for any other tool but once you realize the convenience and things you can do with them that you can't do easily with any other power tool, the oscillating tool becomes an indispensable addition to your tools.