The Mortars are obvious, but someone asked me to compare one of the other units (overlord) so here's a quick synopsis.
Comparison of EpicUK Baneblade to EpicUK OverlordReasons to compare:
They both have armour 4+, both are reinforced, they have the same Damage Capacity, both have mixed weapons and maximum range of 75cm. They also come from Strategy rating 2 armies and both are 2+ activations.
(No comparison between units in armies is ever perfect, but this is probably an acceptable comparison to an existing unit)

They are both extremely survivable vehicles vs anything other than TK.
Areas the Baneblade is better:
[] It costs 50pts less (200 vs 250)
[] Easier to hide
[] From an army with Commissars
Areas the Overlord is better:
[] It can skim over terrain
[] It can see over terrain pieces more easily when firing
[] It is faster
[] It is immune to Close Combat
[] It has built in Anti Air
[] Damage output vs tanks at range 75 is between 3 and
6 times as good (usually the latter, there is rarely a reason not to ensure the target is directly in front).
[] Damage output vs infantry at range 75 is between 2.25 and 4.5 times as good.
[] Damage output at all ranges vs all targets is better than baneblade.
[] It has blast weaponry (short range, not frequently used)
Conclusion:
The new unit (Overlord) is significantly more powerful than the established unit (Baneblade). Its advantages include speed, immunity to CC, built in AA and 6 times as many battle cannons.
Suggestions
The Overlord looks underpriced compared to the Baneblade. Making the Overlord more expensive may not be ideal due to the fact it doesn't make it more survivable.
Instead I suggest the area to tweak is the damage output; Overlord Battlecannons should be 'fixed' left and right, so they can't fire 6 at a single target to the direct front or rear.
This would better match the rules to the model, and it would still have higher damage output against all targets at all ranges than a Baneblade.
Just suggestions.
