This build looks really weird if you don't know how this weapon works.

Every time you increase your combo counter (your combo is at 59 with a x2 multiplier and you hit 5 guys for your combo to go up to 64 with a x3 multiplier, this only counts as one time since it's just the multiplier that matters) you gain 4% Heat that does not mix with other elements for 15 seconds. This buff can stack up to 30 times. So the problem is once you [Reach] 12x combo you've only gotten 12 out of 30 stacks, so you actually want to be able to lose combo so you can build it back up for more stacks. Now lets get into how this build helps you do exactly that.

[Focus Energy] + [Focus Radon] > [Galvanized Reflex]

Heavy Attack Efficiency allows us to use Heavy Attacks to get rid of some of our combo without needing to constantly restart from 0, but the effect caps at 90%. This is why [Focus Energy] is actually more ideal than [Voltaic Strike] or even [Shocking Touch] as it both gives us the Electric damage we need and 40% Heavy Efficiency.
We could get the full 90% by using [Galvanized Reflex] but the initial combo bonus is wasted. At full combo a heavy attack at 90% Efficiency will leave us with 198 combo allowing us to quickly get 2 more stacks. However, the 40% from [Focus Radon] getting us up to 80% Efficiency will leave us with 176 allowing us to get 3 stacks per heavy attack instead. This makes building stacks slightly faster while also giving us slightly higher damage with the 60% Radiation and gives an extra status for [Condition Overload].

[Amalgam Organ Shatter] > [Galvanized Steel]

Unfortunately while [Galvanized Steel] gives a lot more damage we really want to run [Amalgam Organ Shatter] since we can't run Tennokai mods for our heavy attacks as we need them to actually drain some of our combo. You could run [Galvanized Steel] if you prefer it but I find the slower heavy attacks very annoying considering we need to do one every 14 seconds or so.

What do I use instead of [Primed Fury] if I'm using a frame with attack speed buffs?

[Galvanized Elementalist]. A LOT more damage and more status chance.

So what makes this weapon worth using despite all the micromanaging?

The heat buff not fusing with other elements means we have 120% Heat leaves us with Heat as our primary status while still being able to spread the Heat status with melee Influence. It also enables a playstyle that allows you to use heavy attacks (that apply forced slash procs btw) pretty much whenever you want.
The [Tonkkatt] are quite powerful when you know how to get the most of them though.