I can’t comment about Drones Direct but I would stay well clear of Gearbest. I ordered from them once, and once only. I ordered a £200 item that was DOA. They would not refund my money but instead tried to offer me £10 in store credit as compensation. As I’d payed by PayPal it was PayPal who refunded me and told me not to return the DOA item. I think GB are on their way out. Their store front is very depleted compared to a few years ago and they’ve not been active in the RCGroups Gearbest support thread for at least the last six months.
I’ve used Banggood quite a bit with only one minor issue that was resolved quickly. I wouldn’t advise buying a DJI product from them as I believe DJI will only honour the warranty in the country it was sold.
5GHz WiFi was a big issue for Android EU users when the Spark was released. The Spark was only equipped with four 5GHz WiFi channels that were not available for use in Europe on Android phones and DJI didn’t support the use of an OTG connection for the Spark at that time. This meant that to connect an Android device to the Spark controller the user had to use 2.4GHz and use the much shorter range 5.8GHz@25milliwatts for the controller to Spark connection. After about six months of protest in the Spark support forum DJI enabled OTG connection but still claimed they didn’t officially support it. You shouldn’t have any such issues with the Mavic Mini as that has a cabled connection for both Android and iOS built into the controller.