So you prefer girth to length, eh?
I cannot speak for every ego on the market, but I have a 1300 mah SMOK E-max. It's just like the twist except it also has variable wattage (instead of just voltage). It is longer and fatter than the average ego battery. The mini protank looks kinda weird on it because the battery is fatter than the
tank. Same thing for the SMOK Aro tank. Standard 510
tanks would probably look better on it, tbh. The battery itself is about 5 inches long.
Word of caution about this battery: while it vapes fine and the battery does appear to provide 1300mah of
vaping time, it has its idiosyncrasies. The "low battery warning" light does not work properly. This is a problem with pretty much all of the batteries (I googled it and found lots of people with the same issue). When you get the warning light, the battery is dead (which makes a "warning" useless). It's not a big deal because after using it, I know how long I can expect it to last (about 10-12 hours for me on 8 watts. I vape HEAVY). More moderate vapers get 2 days out of it. People who use it sparingly (like say on lunch breaks and after dinner) would probably get 3 or more days from it.
It also is tricky to charge. The charge light (on the charger itself) will show orange when it's full instead of green. This is also an issue many people (and not just me) have. But this also depends on the charger. It behaves weirdly on some ego chargers but not on others.
But other than these two nuisances (which aren't a huge deal if you know to expect them), it is probably worth about the $30 you will pay for it. This battery is definitely fatter than a standard ego and a full size protank would not look as out of place on it.