Difference between Shimano HG51 8-Speed Cassette and Shimano HG50 8-Speed Cassette Can anyone tell me the difference between Shimano HG51 and HG50 8-Speed Cassettes?

I can't find any information online about this so was hoping someone might be able to help me.

I am looking to replace the HG50 8-Speed Cassettes on my mountain bike but searching online there don't seem to be many about and they are more expensive than the HG51 which seem to be in higher supply as well. So I'm thinking of buying the HG51 to make some savings but not sure if its compatible, I'm thinking it might need a different chain to the HG50 or something?
The only difference is the model number, and the year of the design. They are fully compatible, assuming the number of gears is the same, and that you buy the appropriate match to your bike. The road version is Tiagra 8 speed. The mountain/hybrid version is Alivio 8 speed.