Background.
With his career in the Blood Angels cut short thanks to a Xenos blade, Zephon was sent to Terra as one of the Crusader Host. His new bionic limbs didn't integrate with his remaining flesh initially. Until Land himself too an interest in Zephon. Land fixed up his bionics just in time for the siege of Terra where he rejoined his legion whole heartedly.
Strengths.
Zephon is a Master of the Legion with everything that that brings with it. His warlord trait means that he chooses a destroyer squad as his own personal retinue and they all gain the chosen warrior rule. This is not very powerful, but fitting given the background of the character.
Zephon's main strengths are in close combat. His AP2 S5 hits will cull many enemy squads, whilst his jump pack will mean his is more than a simple distraction -- he has the potential to insert himself (and his squad) just where needed and cause a lot of havoc. He comes with rad and melta bombs as standard, along with artificer armour and an iron halo.
Weaknesses.
Ranged weapons are not Zephon's strength here, although the 10inch range S5 gunslinger will do reasonably well before charging. Blind and Deflagrate are just the icing on the cake.
Overall.
Zephon is a commander with a very specific style: close combat and destroyer squads. Take a good quality destroyer squad with jump packs and he is ready to cause mayhem wherever the controlling player wills it. He is a strong choice for the Blood Angel loyalists and will perform well for the points cost. There is no much not to like here, and candidly, I would dread playing against him since the rad grenades make things tricky. I'd probably be thinking of large vindicator pie plates or massed arms against him and his squad. But then again, he'd stand a chance of surviving and massacring whatever shot at him. Seriously: Zephon is a good choice for a particular Blood Angels style of play.