EverDrive is pretty great. The prices are definitely premium, but you do get a reliable, quality product. Just make sure you're either buying directly from Krikzz or an authorized reseller. There are a lot of clones floating around on certain sites (such as AliExpress) that are of varying quality. Additionally, the clones usually run a hacked firmware and trying to use the official firmware will brick it.
It's worth noting that the N64 and Genesis both have proper EverDrive alternatives. For the N64 there's the SummerCart64, which is an open source project and seems to have some features the ED64X7 doesn't (like 64DD support). As for the Genesis there's the MegaSD from Terraonion. I haven't used either of them, so I don't have much of an opinion on which is best.
It's not tentacles. A futanari is a woman with a (usually rather large) penis.