Without wanting to play my own harp, see https://forum.amsat-dl.org/index.php?thread/2856-transverter-pe1cmo-and-kuhne-down-konverter/&postID=9489#post9489
I don't know if Megasat has a good representation in the UK, the BRexit has caused a deep ditch to the mainland but let's keep the forum technical please!
However, brand and type doesn't matter that much. Keep in mind that if you buy a certain type of LNB, and you order the same type 3 months later, you will likely find completely different electronics inside. In that regard, what does matter is to "buy a few at once". If you break one, you have learned the construction and the next one will be easier to modify\; you also have "one to look at" which I find, helps a lot.
The key is to get a LNB with crystal reference. The good news is that these are cheaper than older models with DRO. My suggestion is you buy a few, open one, if it is a DRO-type, send the other ones back unopened. Personally I find it difficult to ind DRO LNB's these days; PLL is much more common