To go back to the OP’s question, my recommendation depends on:
- what other 5* greens you have, if any
- how often you summon
- what other maxed 5* you have
I intend to give tonics to my hatter, but Lianna (a recent addition to my bench) got her tonics instead of Hatter. And I have Alberich, Tarlak, Evelyn, Zeline and Gregorion maxed.
I think Hatter is a very nicely balanced hero. Fun, different, but not overwhelming. In the right battles, he’s great. In other battles, not so much. I put him in the middle of the pack of 5* greens behind the first four listed above and Lianna.
The trouble with Hatter on defense is that it’s too easy for someone with a decent bench and half a brain to work around his buff-steal. Don’t bring buff-happy heroes, and delay activating buffs until he’s fired. There are a lot of excellent choices among heroes that don’t cast buffs! Arguably the meta now leans towards heroes that cast debuffs (e.g. Evelyn, Santa) rather than buffs (e.g. Ares, Aegir). Guinevere is an exception, but I never use her on offense.