Hey thanks everyone,
following the advice on this thread and throughout the forum I went with the ALFA AWUS36NH because it has RT3070 chipset, detachable 5bi antenna and 2W power (that is just within the Slate’s capabilties).
I will not be using the internal 2.4ghz at the same time so I expect the combination to be reasonably stable.
I found the adapter for 27 Euros which is on the higher end of my margin but I expect that it will be less likely to disapoint than the other options and it will be easy to upgrade with another antenna in the future.
I did like the idea of the OEM rt3070 with big antenna but I did not want to get a potentially junk product with less potential for modification in case expectations fell short.
In retrospect, I think that the Slate does have good WiFi already so this is why I really wanted to get the best device to be sure to see an improvement. I am not really sure that some of the adapters linked would have genuinely provided a tangible advantage over the Slate’s built-in wifi.
I might post back once I have received the device if there are some interesting results/observations.
Thanks again - I guess we will have to wait and see 
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