i keep 10-20 in my army camp I love them.
I use a relatively cheap army composition Bar/Arc/Gob/Wb
usually barbarians and archers are enough to take out majority of their air defence capabilities and then minions are used only to mop up. Ie bases with Mortars in centres instead of wizard towers.
Also great to clear sections of bases not covered by Archer towers. or just to help your barbs destroy that wizard tower quickly as the barbs cant take too much wizard tower fire.
I'm working on DE to upgrade to Lv4
I find they work better with 10 minimium, 5 isnt enough to overwhelm 1-2 archer towers. where as 10 is enough to destroy quickly.
They're actually pretty good and especially with farming. They can be made in the dark barracks so it's quicker to make farming troops with the extra 2 barracks, and the fact they're airborne means they can swoop in and take out mortars and other things while the ground defence can't touch them if you clear the way a bit. Their only drawback is the 2 troops space so you need to find a nice balance in your setup but they do work well for me lately when i've used them.
I don't use minions because their DE cost will add up trust me
And even if I did I want to upgrade them now for 10k DE (which I do have) and I also have a research finishing in 2 hours but i'd rather upgrade other troops I use more and my BK which is much more worth it in my opinion