The Kaiser Class Battleship should be seen as the starting point to understand German engineering and design.  This class is built upon the premise of being hard to bring down.  Armor, armor hull, and spread out, saturation fire guns in turrets means that these ships are designed to take a beating and keep flying (and firing).  

However, the ships of this class all suffer from slow speed and poor maneuvering, with limited options to change facing short of doing a full stop and turning in place.  Their guns, while respectable, don't have the greatest range, or the best crews.  Their slow speed and poor turn radius make them especially vulnerable to torpedoes, though some of the ships have been retrofit with chaff to mitigate this weakness somewhat.

A standard question in shipbuilding is to ask how well protected a ship is from it's own weapons.  So how does this ship's armament compare to it's protection?  The Kaiser is well built to be moderately protected from it's own biggest guns, assuming it is a moving target.  The average armor value with the undamaged armor slots means that any given shot is less likely to do any damage, especially on the sides, as long as it isn't being attacked from the rear.  Even including crew dice, a standard shot has less than 50% chance of doing damage.  It should be noted though that this assumes the ship is moving.  If you have to turn the ship, with an enter hex value of 3, you have to do a full stop to spin in place, unless you have the Hard Burn or Commander Admiral Cards.

The Kaiser has only main guns, and no secondary weapons, but it has pretty good main guns.  The 24cm cannon fires a Red die out to 7 hexes, and a yellow beyond that, and are all Saturation Fire guns, and Turrets, with Green crew.  So if you have an enemy ship in your broadside, you'll be dropping 4 Saturation shots at the enemy.  Given that these shots all ignore "miss" results, this makes the ship absolutely deadly against destroyers and lighter cruisers.  With that in mind, the lack of a bracketing gun means that they may struggle to penetrate other armored targets.

Even without some of the Kaiser's armor, the Kaiserin is still a very heavily armored ship, with better than 50/50 odds on inbound shots before factoring in crew skill, being nearly impervious to bombers, and able to even tank standard torpedoes in a pinch, which is good as it still can't turn particularly well.

The Kaiserin's addition of bracketing guns on the broadside makes it a better battleship hunter than the original Kaiser.  Bracketing all 3 guns together gives you an average roll of 7.5 at long range, or 10.5 at short range, much improved over the 1dRed's 5.5.  If your goal is stripping armor off an undamaged flagship, these are the guns you want to be using.  This also combos well with a Bracketing Crew ship like the SML Grier or Falke.

The major difference verses the Kaiser is the fore armor not being good enough to reliably turn into a torpedo, but the broadside armor remains reliable against most individual shots.

There is nothing about the Wilhelm I's guns that make them meaningfully different than the Kaiser's.

The Friedrich Der Große has nearly the armor of the Kaiser, though not quite enough to hit the break point against crewed 24cm shots.  But what it does have is much better chances against torpedoes with the chaff slots.

While it has less 10.5cm guns than the Kaiserin, pairing this ship with a Bracketing Crew ship like the SML Grier or Falke will make it's secondary weapons sing.  Even without support, 2 Blue dice at 7 average is marginally better than 1 Red die at a 5.5 average for punching a hole in a heavily armored target.  Longer range the advantage drops off somewhat, with 5 average for the double green dice, Fred wants to get close to it's opponent.

These ships are built like bricks, and unfortunately drive about as well as one.  More than anything else, these ships need a speed increase like Hard Burn, if only to be able to turn without doing a full stop.  They will be very easy to predict where they are going and what they are doing, and as such are at risk for torpedoes and being out maneuvered.  They are also under-gunned compared to other Battleships with a limited number of shots with guns that would struggle to crack their own armor.

Ratings:

SML Kaiser: B-
SML Kaiserin: B
SLM Wilhelm I: C+
SML Friedrich Der Große: B