The Helgoland class were the second class of dreadnought battleships built for the Kaiser's navy. While the Nassau class were the prototypes, the Helgolands were the more mature edition, Nassau 2.0, so to speak.
... but you do get the benefit of an extra half unit, so you can equip either a 75 round stern gun, or (more likely) a 75 round stern sidemount. This will provide some nice extra firepower in a place where you can really use it.
Helgoland is a 28 second ship, and with the same three shaft arrangement as the Nassau, will have less acceleration compared to a four shaft ship.
However, also like Nassau, the Helgoland has the same excellent triple shaft and twin rudder arrangment on an even tubbier hull. Built properly, she should spin on a dime.
The Helgoland is also quite a bit longer than the Nassau, and as a result has a greater length to shoot at, along with less of a casemate effect. It's still significant, but Nassau and VU are both better.
Much like the Nassau, the Helgoland should be very beginner friendly, especially since she has a little more hull volume to work with and weight, so you're not constantly fighting the limitations of a tiny battleship. Likewise, while not quite as small on the water, she's still hard to hit and with the extra rounds, carries a bit more of a wallop. More experienced battlers will still probably be frustrated by the lack of speed, however.
I like the Helgoland, and if someone offered a good kit for one, I'd probably recommend her, maybe even more than the Nassau, due to the fact that she has a bit more firepower and staying power. The ones I've seen on the water so far have seemed to be quite decent, and represent the class well.