First of all - there are no published statistics regarding the turret or the sponson gun was used more for both the Char B and the M3 Grant/Lee.

That said, the sponson gun was the larger and longer-ranged of the two guns on the M3 (the sponson was a 75mm gun, the turret was a 37mm gun), so it would not be out of the question for crews to prefer using this gun.

As for the gun usage, the general idea for both the Char B and the M3 Grant was that the turret gun would primarily be an anti-tank weapon, whereas the sponson was an anti-infantry/fortification weapon. In practice though, particularly with the Grant, both were used against tanks.

The Char B, doctrinally, was supposed to be a heavy breakthrough tank - assigned to French Armored Cuirassier Divisions which were attached to infantry armies that would attempt to assault trenches and fortifications.

The Grant meanwhile was a medium tank based on American doctrine - meaning it was primarily meant for infantry support and exploitation, but also tank vs tank combat if necessary.

There really weren't very many designs like this. The Char was something of a freak that was the result of the convoluted French armaments industry, whereas the Grant was a strictly stop-gap tank until the US could build the tank they really wanted - which was the fully turreted M4 Sherman.

And the reason for this was simple: Multi-turret tanks were simply too unwieldly in the field for one tank commander to control. The ultimate examples were the Soviet T-35 and T-28 tanks, neither of which saw much success.

Was their combat doctrine to use the tanks as assault guns with a higher profile using both turrets to suppress their enemies with rapid fire, or as a heavy tank?

Just wanted to point out the Char B1 didn't have two turrets. The hull mounted gun could move up-down but was basically stuck pointing in whatever direction the tank was pointing in.

On another note, is there any other armoured vehicles with similar design characteristics?

There were some others. The Russians went through a strange phase where they were obsessed with putting lots of guns/turrets on everything. See the T-28, T-35, T-100, and SMK as examples.

The early versions of the British "Churchill" tanks had a 2 pounder (40mm) gun in the turret and a 3 inch howitzer located in the hull. Like the B1 the hull mounted gun had very limited traverse and generally required pointing the tank right at the target.

The Japanese Type 95 had 70mm and 37mm cannons mounted in separate turrets. However the 70mm was the 'primary' weapon (i.e. the one located in the top turret that could shoot in any direction).

In a slightly more esoteric example - there were Sherman tanks where the 'bow' machine gun was replaced with a flamethrower.