Actually blend shapes in UE4 are no more an issue in terms of memory usage and you can use them however you want…A Boy and his Kite is the perfect example, if I’m not wrong 3lateral created a blend shape rig with hundreds of blend shapes and Epic itself encourage developers to use blend shapes in their rig…
Blend shape are very easy to animate and you can animate them also directly inside UE4, which is something that you can’t do with a joint based facial rig…also don’t forget you can trigger normal maps dynamically which is a built in function inside UE4 
Anyway it’s up to you which one to choose…if you like soft selection modeling go with blend shapes, if you’re good at skinning try bones…
Or you can use bones with blend shapes for correctives and you’re done