The value of these is... not high. When you take into account the loss in base stats, MLB Diabolos is no better than the typical 40% character attack 20% HP eidolon, which are much easier to obtain from the Eidolon orb shop. MLB Bugbear is situational, when you need a big HP boost without a large tradeoff in character ATK. Meng-Huo will suffice for heavy HP checks, and 40/20 eidolons are good enough for most other HP-sensitive situations. SSR weapons with +HP should already be a standard part of your arsenal. I don't really see any situations where I'd say "If I had a MLB Bugbear, I could've cleared this..."