It should be O.K., but check if it has perlite in it. If it does be prepared for the perlite to drive you crazy floating around the top of the tank every time you move plants. I've also learned the hard way to get as much of the wood pieces out of the soil as is humanly possible. If it's not removed it will stain the water a weak tea color (not a problem if you don't mind that the tannins are good for the betta) and it contributes to the gas pockets formed in the soil.
Personally when I did a NPT I found that the gravel just wanted to sink under the soil when I was poking the substrate, or moving plants. I liked it better when I finally got rid of as much of the gravel as possible and switched to sand. As far as fish waste goes, you don't want to over clean a NPT, the bacteria in the tank converts the waste into nutrients for the plants. If you have everything in proper balance all you'll really want to clean is the top of the plants. If you like a neat and tidy tank then skip an NPT, the mulm and stuff that it'll develop in the beginning will drive you crazy. If you want cory cats then they will really appreciate a sand substrate.