While lacking in terms of attack, this deck offers many forms of card removal through the effects of it's fusion monsters. Monsters in this deck can also protect and give additional effects to each other by union equip.
Equipping union monsters is a big part of this deck's strategy. The monster that is equipped with a union monster gains protection from being destroyed, by destroying the union monster instead, and also gains additional effects based on the union monster equipped. Use Roll Out! to equip a union monster from your graveyard to an appropriate monster on the field.(Take note that a monster can only equip one union monster at a time.)
I've been toying with this deck a lot recently. I think Heavy Mech Support Armor is not that good, and instead I use Heavy Mech Support Platform. This is because this deck generally lacks in the ATK stat. For this reason, I'm using only 2 Frontline Bases and 3 Roll Outs, since reviving Union monsters that buff the ATK of your monsters is so valuable. Roll out is the real MVP of this deck imo.
Also, I use Sleight of Hand as a skill, since it helps you get that much needed ATK, plus it gives something to discard if you have something to target with your fusions.
Also, no Enemy Controllers, use Sphere Kuribohs instead if you have them.
Considering XZ is able to remove face-down backrow card, and another union monster adds 500 ATK DEF and extra life for the tanks, I guess sergeant electro and RMM are not that significant changes... if consider union interactability, I'd prefer the machines
Ectoplasmer destroys both monster and union... Is this a glitch?
I am a fan of the principle of the union deck. You'll find that your backrow is always clogged. Without having 5 zones, this deck is weakened severely. With 5 zones, you could keep each monster protected from destruction 2-3 times a turn. With just 3, it becomes tough to not have a full backrow. Great draw speed. Great revival. Great card removal. Solid Attack. (X-canon plus union can get you a 2200-2400 monster turn 1) The only downside is a clogged field. Which always happens since you don't win in a couple turns.
for this reason I would limit the number of continuous spells in this deck from 4 to 2, and include a sphere kuriboh (or two) for defense. also, roll out seems decent but there are probably better cards for defending your union monsters (windstorm, mirror wall, enemy controller)
This deck is not as good as it stands now.. I've personalized some cards (about 3 or 4) to add SRH and ECON w/Kuriboh. You will want to keep the Frontline Base spell card however.