(Deka Gel-tech) is correctly charged at (2.35v/cell)14.1v with (2.3v/cell) 13.8v float @ (68°F) 20°C.
A500 is gel... Gel deep cycle, 14.1V (2.35 x 6 cells = 14.1V)
.Sonnenschein/Dryfit (German) A200 product is correctly charged (@ 2.4v/cell)14.4v/ and float voltage is (2.3v/cell)13.8v) @ 20°C
A200 is different and not a true gel or true deep cycle battery and so less cycles. And cheaper. And 14.4V
Sonnenschien own chargers on the link you posted have a SWITCHABLE output to suit 14.4 or 14.1 for gel. Take a careful look:
Battery Type selector switch for proper charge format for specific battery technologies
You can, and many do, charge gel at 14.4v.
But you DO lose some cycle life. Its not ideal. And this includes almost all mobility chargers.
Sonnenschien and MK use the same technology in their true gel deep cycle traction batteries. In fact Sonnenschien licenced it to MK...
And both these companies say you can charge at 14.4v. Because they would lose battery sales if they restrict it to 14.1V only. But if you look a lot deeper, it is at the expense of cycle life. In fact in marine use all of this is well known, and marine chargers generally have a proper 14.1V gel charge setting as do most industrial or large solar chargers.
Gel BEST charge voltage for cycle life 13.8 to 14.1V
AGM generic 14.4 to 14.6V
Pure lead like Odyssey, Optima, and some Exide spiral cell batteries, sears die hard rebadged ones are 14.4 to 14.7 where 14.7 is best. And to a very low A cut-off point.