I just got one of these, and I cant seem to get more than around 1000kB/s, but on an older cam (Hikvis) I see over 2000 in BI5 is there an issue here? Are Reolink not very good cams?

Reolink tend to be ..interesting.. with Blue Iris. Some manufacturers cameras just work, but Reolink tend to need fettling. Make sure you are not using the + version of H264 or H265.

Check the firmware version for 'Fixed Frame Rate' at the top of the Stream menu. If it's not there, upgrade to the current version.

You're stuck with H.265 at 4K which sucks in both Blue Iris and Reolink implementations, imho. If you're running an Intel box with a Gen6 or later iCore processor, QuickSync can be your friend and should at least be tried if it's not already set as the default CPU/GPU in your BI config.

You can get an 820 to work, but some would suggest they're not worth the hassle. I have some 810s which are the bullet version or the 820 and I actually like them up to a point.
But I got 4 of em for 60 bucks so I got what I paid for, too. LOL

While the night time performance is a bit lacking, you'll probably like the 820 if you have the patience to get it dialed in.

I am using a Trigkey Mini PC with AMD processor like this https://www.amazon.co.uk/gp/product/B0BCVGPG5J

What should I select as the HA decode on this?

Looks like a cool little box.

Good question on the HA.