I have no issues in my newer 44g pentagon.. Or using my older like 15 year old 27g hexagon.. Both tanks are 25 inches tall.. The Hex is 18 inches deep on all corners, and the pentagon is 25 inches deep and 30 inches long.
The only issue with my pentagon is i cant quiet reach the very back of the tank i had to get a little 1-2 foot tall item to stand on to reach plants in the very back.. My hexagon i have no issues with its the the height plus depth on the pentagon..
As for lighting... and flow.. I have no issues lighting my Hexagon.. I have 2 old T8 light fixtures you know the ones you get standard buying tanks i tore the guts out of one and wired a duel Power Compact ballast so my 27g hex has a duel PC light my plants are growing great and the entire tank is lit up perfectly.. I put the other T8 light near the back with a plant grow bulb since its dim as a sort of transitional light when i turn the lights on and off so i don't spook my fish..
My pentagon is a tad trickier to light but i have a duel power compact fixture over it (4 lights essentially ) and it sits about 8 inches above the water line it fills the entire tank with light.. The only issue is the very back isn't lit on the top because of the deep tank so i have a 14 inch T8 back there to get the top lit.
As for water flow and so forth.. I have no issues ? I have a top fin internal 40 in the tank and its got a spray bar on it i can turn it 360 degrees in the tank.. If i want a complete whirl wind of water flow in the tank you just turn it at an angle on one of the pieces of the glass and due to the almosyt circular shape of the tank it makes well a whirlpool effect in the tank. not powerful like a whirlpool but you get the idea lol.. The reason anyone would say they have issues with flow in these tanks.. is because they are using HOB filters.. and power heads... the internal filters eliminate the need for powerheads and are much much quieter then HOBs
I like tall tanks.. Like someone stated, with tall and deep tanks you don't have to sit in the chair or bend over to look at the fish.. My moms 30g tank for example its a typical 30g 36 inches long and so forth but its so short what like 16 or 17 inches tall that you have to bend down or sit in a chair and bend your neck down to look at fish on the top of the water.. I don't have to do that with my pentagon or hexagon.. The 55g is well in between.. And while i agree some fish need the length of say a 40g breeder or 55g tank.. The problem with these tanks is they are too darn shallow.. 12-13 inches deep ? I don't like my 55g because you don't have much options as far as placing wood or plants go and fish cant only really swim left or right and that's it..
With my pentagon its 30 inches long so its got some length but with it being 25 inches deep and tall my fish can swim 360 degrees in any direction....
Now i have seen some REALLY tall tanks like youre talking about.. i would think anything higher then 30 inches is too much unless its like a 200g tank. Ive big ass hexagon tanks that are like 36 inches tall but they are still only like 22 inches deep on all corners.. That's just too tall and narrow
This is my newer pentagon 44g.. Plants still need to grow out