How many GHB/TT units have you fully merged up

Fully merged..? To +10, or to the max possible merge at this moment in time?

Lyon, Marisa, Joshua and Valter
They are all already +2/+1 on this moment.

I have all the free units at 5*, but only Masked Marth, Black Knight, KannaM, FH!Takumi and Garon are at max free merges. I haven't used the free heroic grail yet, as I want to see if they plan to give us more copies for free with reruns first.

As merged GHB and TT units i have

Arvis+4
M!Marth+3
Black Knight+3
Xander+3
Joshua+2
Aversa+2
Camus+2

I don't know when and how i lost one copy of Camus, otherwise he would be +3

I have M!Marth +2, Arden +2 and Black Knight +1 as my only merged TT/GHB units, with some others promoted (but without merges) like Camus and Xander.

(If I didn't have so many units I want to build up, I probably would have more merges on more of those free units.)

Quite a lot, but my highest is Zeph. Give him the golden crown, and is great unit for Aether Raid because you can put him behind a wall so people are force to use range units.

The initial Grail costs aren't too bad. What's really going to hurt is the gradual increase in costs per usage of each unit. So far, most GHB/TT units not named Masked Marth cost around 2200 to max. Currently, the only income of of Grails is from Aether Raid chain and 'end of season' rewards, which only gives out up to 80 per season. Hopefully they'll give us more opportunities to earn Grails in the future, because otherwise, the grind is going to get really grueling.