Congratulations on 73
PLD AF was the best AF since every pld can wear it until they switch to Koenig/Crimson for HNM. There was nothing better than PLD AF for a PLD.
However, the Adaman came out, it is expensive, but in exchange, it's worth it. When I bought mine, they were 4 millions+ all together. It took Kailyn and I 2 weeks to get the full set.
Here's a compairson of the stats:
Gallant: DEF135 HP73 VIT4 MND/AGI/DEX3 Enmity8
Adaman: DEF158 HP27 MP30 VIT14 MND4 Enmity11 Evasion-4 AGI-2 INT-1
PLD has low evasion as it is, so losing another 4 won't break you. AGI - being a hume, even with -2, I still have more AGI than an elvaan pld with 2 drone earrings. So, not a problem there. INT.... you tell me :P
However, what do you gain by switch over?
22 DEF, 10VIT and 3 Enmity. Those 3 stats is huge when it comes to play the main tank role. You need to be able to take hits and hold agro. On HNM, you won't hit for jack anyways, so dex isn't really an issue there. The extra enmity comes handy when you only rely on ja and flash to hold agro.
Now, let's talk about hp. The true down side about Adaman gear is the hp lose. You will gain 30 mp but you'll lose 46hp. How to counter it? You just have to use hp gear rather than agi on earring slots or any other you can think of. I am really lucky that CKD got me a Cassie earring. It's 50mp->hp conversion. It basically makes up my hp lose by using the adaman armor. I'd suggest use pigeon earrings or +1 if you decide to switch to Adaman until you can get a cassie earring. I use Cassie earring + pigeon earring when tanking HNM, Cassie earring and Knight's earring in xp pt for extra VIT.
Now, back to the original question:
Is it worth it? Yes
Is it necessary? Sorta
Do you must have it? No
I wouldn't say Adaman is a must have when you are in xp pt. But if you plan to be the main tank for a HNM LS, it's really good to have due to the Enmity, DEF, and VIT gain. I also use Mermaid's Ring when I can't use Bomb queen ring or Jelly Ring. enmity+2 on the Mermaid's Ring.