4+10 guide

As content clearers, they work great. I wouldn't use them in arena, though, since you get a fair bit more score for a 5 star, as far as I can tell. If you have your arena team already, go for it.

Nowi is the only one of those I'd say try to 5*+10. Her Arena score when maxed out and weapon refined is over 200 which is great for a non-armor unit.

You should really 5 star the Tiki and Nowi, they are great in the arena, Priscilla and Corrin could be a good choice for 4-star + 10 to be a de-buffer and for a healer

All good, I would also 4+10 Lukas, Beruka, and Sheena. They are all amazing walls.

If you're looking for units to make a serious arena team, you need to 5 star each of those you want to use and then slowly work on merges if you want to be able to stay in tier 20. I'm F2P and currently working on +10 5* Tiki (A) and Nowi, in addition to my already finished Cecilia Raven TA build, so as to cover anything the arena throws at me. Then I just need a bonus unit to be able to score highly in arena and hopefully stay in tier 20. Fae would also serve well as a green +10 unit, though she doesn't cover Brave Lyn quite as well as Cecilia does.

Good units to 4* +10 would be F Corrin, Cherche, Olivia, Hana, Donnel, M Robin, Oboro, Sheena, and Eliwood. But I'd prioritize having a solid arena core team first, similar to the one I'm finishing.