R4, R4U what's the difference ?

I had a question to anyone who can answer, whats the big difference between original r4 and R4U, my r4 kernel stopped at v1.18, couldn't I just download the R4U kernel to reap the Ultra's benefits ?

no, the hardware is different

Hardware is different, the original R4 is THE original, it'll work best. Those all other copies, like the R4 III, R4 Upgrade, N5, etc. are called clones. They can even damage your DS. Also, the R4 is not a recommended card by all means at the moment, as its team has stopped producing firmware and have abandoned the R4 work.

dimitric12h16n2I had a question to anyone who can answer, whats the big difference between original r4 and R4U, my r4 kernel stopped at v1.18, couldn't I just download the R4U kernel to reap the Ultra's benefits?

The original R4's firmware has stopped at 1.18. I am not sure, but I think the R4 clones' firmwares can't be used on the original firmware.

Clone firmware on an original card then generally no.