BUTTT dooo I want to spend this much, I wish I could see a video of someone with 20 mobs n them, I wanna see the tp gain.
You should get it, you won't regret Gandring because it is ultra fun for THF and gives you something different to do. I was gifted a Su4 and I use it in Omen and sometimes Sheol A farming, and have a blast doing it.
In omen, I can pull the first 2 floors on THF solo and clear it in about 45 seconds (just engage a trans first and run around so your whm trust heals you). The "small light" path I usually pull the rabbits and mandys through initial aggro, then pop flee and pull lizards/vultures, and if it's daytime, Ladybugs. By this point, flee is about to wear off, and you can die very easily if you get animation locked or not healed (because with so many mobs, targeting is terrible), so I pop Perfect Dodge right here, Waltz myself, engage, then fire of AEs. I'm able to kill those 5 groups in about 3 minutes from pull to death, but it's very fun to do it this way. AE is not as effective vs Panopts and Pixies, but I still do it on those also. Doesn't work on Fairies, so I just kill those with Twash.
In Sheol A, I'll go Su4/TP Bonus and pull a pack of mobs and fire off Rudras instead (AOE secondary damage doesn't work in Odyssey), each mob feeding me TP. These are slightly stronger than Swarts mobs from Omen, but they still miss you a bunch, so you get a lot of TP. You basically use them as batteries to give you faster DPS.
Before I had the dagger, I would sometimes pull mass groups in Sheol A/B on THF when we did money-farming parties. The dagger would have been a cool toy to mess around with while tanking and killing the groups of Nostos.
If you can think of a fun use for the dagger, go for it. It's very fun. Its pricy, but it definitely changes THFs playstyle from TP > WS to a more high risk-reward style, and I think it's a great choice. Can't speak to whether its practical in MLs though.