The R4 3DS card is the best choice to play free DS games on all Nintendo 3DS firmwares, just like 3DS 11.6.0-39, 11.5.0-38, 11.4.0-37 and all the lower systems. The R4i Gold Pro, R4i SDHC 3DS RTS, R4i B9S, R4i Gold 3DS Plus are all your choice in UK.
The R4i SDHC 3DS RTS is the best R4 card to play free DS games. It has a really good compatibility, R4 3DS RTS read DS games on all the Nintendo consoles, New 3DS, New 2DS, 3DS, Old 2DS, DS, DS Lite, DSi. With the R4i SDHC card, you can play unlimited DS games with a microSD card. R4i SDHC 3DS also supports homebrews, RTS and cheat.