I have not experience with cartridge filters, but I imagine they are pretty similar. The OEM is likely one of the name brands Unicel/Filbur/etc. There is a chance that the cheap ones are also built in the same factory.
Depending on how different the price is, might be worth a try. They will all certainly work, but there is a chance some may not work as well as others.
Just like everything else out there, there are generics ... should be the same, but might have minor differences. At least this is not as important as a car oil or air filter which could result in expensive repairs ... your spa just may be a little less sparkly.