There is nothing available as small as the "flashq" that works as a flash.
The Canon 90EX as it is the smallest flash available that is fully compatible with your 5D Mk II. It has just a little less power than most built-in flashes

Canon 90EX
Power: Guide No (ISO 100) 30'/9m (at 24mm)
Size: 1.7" x 2.0" x 2.6"
Weight: 2.570 oz. with two AAA cells
(1.8 oz. empty)
The 270EX or 270EX II is also fully compatible with your 5D Mk II, is only slightly larger, but has much more power. It also recycles faster and has a tilt-up head for bounce flash.

Canon 270EX
Power: Guide No (ISO 100) 89'/27m (at 50mm) 72'/22m (at 28mm)
Size: 2.6" x 2.6" x 3.0"
Weight: 7 oz. with two AA cells (5.6 oz. empty)
The 220EX is also a pretty good option. It recycles faster because it uses 4 AA batteries but that also makes it a little bit larger and heavier.

Canon 220EX
Power: Guide No (ISO 100) 72'/22m (at 28mm)
Size: 3.6" x 2.6" x 2.4"
Weight 9.0 oz. with 4 AA batteries. (5.6 oz empty)
How good the flash is is less important
is only true if it is any good at all - a flash that does not work most of the time isn't necessarily better than no flash. \$\endgroup\$