Although the guy in the linked video is clearly a little challenged in many regards, the head is still showing it's own deficits in that video.
Granted, it is also over weighted, but I doubt that the rig exceeds manfrottos rating for it. ( 12 pounds, consider that a SIRUI K40 is rated for 77 pounds and costs less )
Vibration: Notice that at no time does the head actually prevent the set up from vibrating! With an under-powered ballhead the one thing you can do when you are pushing too hard and just need to lock things down solid is you CAN twist real hard and lock it and maybe that will hold things. With the Pistol grips you can't really do that, the spring tension is adjustable, but you are always relying on the spring tension. You can't just torque it down.
Top Heavy: Notice how top heavy everything looks, it's balanced on that tiny pintle, the ball size on these, the actual ball, is diminutive.
Fatigue. Yes, having to maintain a forced squeezed hand to allow motion can actually quickly quickly become fatiguing. As I grow older I find repetitive stress to be a source of constant vigilance, looking for those tasks that will cause me pain. Just shooting a camera has it's challenges, these heads add a HUGE amount of unnecessary additional strain and fatigue. This is my #1 reason to avoid a head of this kind. All my heads and tripods support take strain and fatigue away from the hand held fatigue. I would not invest in support that adds to fatigue vs hand holding.
Awkward to be sure, the handle protrusion is often in the way. For straight up landscape work, it's not bad, though I always marveled that Manfrotto has now made two of this side mounted type and in both cases made it difficult and ungainly to with your left hand, forcing you to let go of all camera controls to adjust. Why not just make them left handed?
The more top heavy (yes even more) classic grip heads were straight up and down affairs,

so either hand would work. They however were even less stable!
Ballhead size = Strength: Ballheads are "classed" based on the size of the physcial ball, 38/40mm is small to medium, 42-50 are the best bang territory, 55/58mm are the largest, anything smaller than 38mm is compact travel. All elese being equal, larger ball = more stable head.
The balls on the Manfrotto (unspecified by manufacturer) is tiny. Maybe 30mm? Honestly it looks even smaller. Not enough surface area to grip.
Cost: These grip heads are not hugely pricey, but the latest Manfrotto is closing in on $200.00 (the old style was more like $99.00) But look at what your paying for. All that metal and how much of it is actually supporting your camera? The vast majority of the cost is going to that Top Gun Joy Stick and trigger stuff, none of which is actually supporting your camera. Put you money into support, not bells and whistles.
Here's a nice pair of reads on ballheads;
MidSized head round up (38/44mm ball)
http://www.dpreview.com …d-sized-ball-heads-tested
Full sized (50mm and up)
http://www.dpreview.com …ans-top-ball-heads-tested
For about $140.00 the SIRUI K30 is more ballhead than a bag full of these pistol grip heads.