Hello, YCM's leading and perhaps only Gusto expert reporting in. I'm here to review your card. I'm afraid I'll have to be perfectly blunt with you: This is borderline useless in Gusto by simple nature of how it works. Because it requires a specific Level of monster (4 in this case, which I'll get around to in a second because this also is significant), Gusto will have a hard time summoning it at all, because as a general rule, you won't have two monsters with the same Level on the field unless you're about to summon Daigusto Sphreez and probably win the game. At which point, you'd rather just summon Sphreez. However, the materials having to be Level 4 in this case is an even greater detriment to Naiadspecter's viability in Gusto, as there are a whopping four Level 4 monsters in the entire archetype.
- Musto, Oracle of Gusto
- Gusto Thunbolt
- Caam, Serenity of Gusto
- Daigusto Falcos
Out of those four monsters, Falcos is a Synchro monster, and not a very good one at that. As such, you won't be summoning him just to ladder into Naiadspecter. Musto and Thunbolt have their uses in theory, but in practice they aren't all that great, let alone in a deck that hasn't aged particularly well over the last few years. Caam is the only Level 4 Gusto monster you could justify running in the current state of the game, and even then, it's pretty iffy. So, 95% of the time, you won't be summoning this card to begin with. This is also a problem that Daigusto Emeral suffers from. If there was no Level requirement, or even if the required Level was 3, that would be a much different story.
The flip effect is neat in theory. You can use it to set and then instantly activate the effect of Kamui, Hope of Gusto... but tragically, that's the only real use it has in this archetype. Kamui's flip effect not being something that you would want to use offensively makes this a bit of a hindrance, but I like that interaction regardless, even if it's highly suboptimal. Also, it can be used to return cards that get banished by the effect of Daigusto Eguls, if you're running that for some inexplicable reason. (Seriously, Eguls is awful.)
However, there is one effect in particular that I really like about this card. The Normal Summon effect. I will reiterate my case about Level 4 monsters, but setting that aside, this is actually really good for Gusto, as a common issue is needing a second Normal Summon when other options that could give you one (i.e. Double Summon) just aren't worth it. This effect in particular really tickles my fancy, because Gusto will invariably load up the graveyard with both Psychic and Winged Beast monsters, effectively making this a themed Double Summon. Which is great! It makes the SphreezTK much easier, not to mention that because it has a downward-facing zone, you'll still be able to summon Sphreez after Naiadspecter hits the field.
I'd also like to briefly go over the difference between this card and Merrowgeist which you mentioned, as well as Emeral, from a flavor perspective. Merrowgeist's effect allows it to shuffle a card it destroys by battle into the Deck. With "return from the GY" effects fairly common in Gishki, as well as Gusto largely having effects that shuffle cards into the Deck (albeit their own in this case), this effect - while not that great on a 2100 body in this day and age - fits the flavor for both Gishki and Gusto. Emeral, on the other hand, has an effect inspired by Gusto (specifically Caam's effect), and one inspired by Gem-Knights (Obsidian in particular). In this respect, Naiadspecter is way off-kilter, as its first effect - while great - doesn't really fit the flavor for either archetype. Its second effect, meanwhile, seems more like it would at home on a Shaddoll card. It's rather bizarre!
Overall, this card has potential to do great things for Gusto, but in its current state, it would never be used in the archetype it actually belongs to. Even Shaddoll won't get much mileage out it, because their Level 4 monsters seldom hit the field and stay on it long enough to summon this.
Gusto Expert's Rating: 5/10, needs work
Closing note: Keep in mind I wrote this review entirely based on its performance in Gusto, as it is in fact a Gusto card. How it will perform in other archetypes would have to be judged by those who use those archetypes.