"Kopaka and Mellum - Unity Set is a good set to start with because it comes with pretty much everything form buying a Toa and a Creature separate. It only lacks a Shadow Trap, but are easy to make as long as you have the pieces and are seen with Umarak at the right of the box.
Mellum is slightly disappointing as he is very similar to Terak - The Creature of Earth, with only a different direction of arm movements and leg length separating them. Instead of being able to claw downwards, Mellum just sits there clapping. Just like Mr Clappy - Axe, Skull Basher
Kopaka doesn't feel like a £15 Toa, more like a £12 or £13 Toa. He lacks the gold that his 2015 counterpart had too much of. The dark blue armor shells are a welcome, as they are new in that color. The arm build is very unique and isn't on any other set, other than a slight reorientation on Pohatu - Uniter of Stone. His weapons, an Ice Blade and a rapid fire Ice Launcher with a small shield attached to it, are okay. The sword is nice and has a cool hilt. The shield - gun is okay, I loathe the stickers, but love the six stud launcher. His regular mask looks the best with the silver melding and the details on the forehead are a nice touch. The mask is also able to have a stud connecting to it, which adds some options for customization. And the golden mask is beautiful and fits Kopaka greatly.
The unity feature fixes a few problems, but also creates some. One, more gold gets added, thanks to Mellum. Two, Kopaka gains a nice amount of bulk from uniting. Three, They work well and don't clash, but instead combine to make a cool combo. The problem is that Mellum's function (when combined) is rendered useless. And hinders arm movement.
All sets have flaws, but this one is alright. And the flaws this one has are nothing compared to Pohatu and Ketar (both sold separately). A mixed bag, but still great. If you are planning to get this set, just get Tahu and Ikir."