If your going to spend £45 then save £10 and get a fire stick its fully supported by amazon for future Android updates and koying the main Android Dev who branched off with SPMC has also done some tweaks for it. Most users spending that type of wonga only want something pre-imaged with the latest addons and we all know there is no 4K on any addons.
If you want true 4K UHD playback at the moment there is only the shield that is future proof they only just announced yesterday that on the next update it will have HDR for 4K UHD and some other minor updates even the newer wetek's wont have HDR on there 4K machines.
Just my thoughts but an amazon fire stick with support for future android updates is the way to go, the Chinese keep bringing out a new machine every few months buy the time people have upgraded they would have spent what a shield cost in the first place.
As @manic01 said just my 2 cents