Is the Tatsugiri + Dondozo combo any good in Reg F?
Its totally viable but hard to play. Dozogiri

has a crazy high skill ceiling and is only really as good as you are in piloting it. There are probably some "free" teams/sets like 2-2-2 or the tera grass camulet variant that can carry you to a certain point on ladder, but is mostly reliant on people not having counters and the bo1/cts format. Against better players and people with counters its going to be much harder to win. Thats where the skill part comes in as to dodge say Amoon

or Urshifu

you gotta position your Dozo

correctly, weave in and out of the spore or shifu and make really good reads. A huge part of this is reads and positioning, theres so many cool mind games you can do like using the Dozo

to bait out attacks and protecting while your partner goes for an attack, or using sub to dodge spores and (something I have been trying lately) stalling out psychic terrain to beat

+

. These are just a few interactions you can use to beat some tough MU's, and with enough practice you can beat pretty much anything but especially against good players it gets really complicated, which is why you see it so little and people have trouble using it.
Early Reg its not as hard to pilot as people dont bring counters as the formats new, but already im facing more competition in tours and ladder as people are building in answers.
TLDR Its certainly a viable strategy but you gotta get a lot of practice/experience to make it work and its certainly not a free or more easy strategy like Psyspam or HO. If you haven't played Dozogiri

before, I recommend not starting now unless you really like it