The Deredeo remains a heavy weapons platform that has its history in the Contemptor class and the earlier styles of Terran and Martian designs. It remained in high demand by both sides of the conflict in the Heresy, although there were few forges that could produce them.
Strengths.
With helical targeting, the Deredeo is fantastic at taking out aircraft with its weapons. Given the weapons, its also fantastic at shooting nearly everything in the game to be honest. Monstrous creatures? Yep. Terminator equivalents? Yep. Its got it all.
The entry level Anvilus auto cannon battery is S=8 with plenty of shots and sunder. The reasonable range means it can reach across the board to ensure they reach the desired target.
The Hellfire Plasma Cannonade is AP=2 at just one pip less in strength and has two modes of firing: sustained, which provides a good number of shots, or maximal, which gives a big pie plate. And terminators are fans of pie, so I hear.
Meanwhile the Aiolos missile launcher gives a huge ranged weapon that can do significant damage to space marine equivalents. Hitting side armour is just icing on the cake.
Weaknesses.
This is fundamentally not a close combat dreadnought. That said, it is still a dreadnought with an invulnerable save and good frontal armour.
My suggestion is to run a Deredeo with ranged terminators -- upgraded with Atomantic Pavaise, it can grant a bonus to the invulnerable save of regular terminators nearby which is very nice, but also costly.
Builds.
Several builds to mull over here, including the ones from Book 5 that I have already noted previously.
Deredeo, Anvilus autocannons, Aiolos missile launcher, armoured ceramite (240 points).
Drop the armoured ceramite if you must, but this is something of a baseline build.
Deredeo, hellfire plasma cannonade, atomantic pavaise (270 points).
I like this one - lots of plasma goodness, teamed up with protective invulnerable saves.