Useful optional extra to the 1825 series of games. 36 extra tiles.
This is a replacement for both K1 + K6 kits (so owners of these 2 old kits do not need D1).
Found this kit to be a very good addition when playing with Units 2 and 3 combined. (We also had kits K5, K2 and half of the tiles from the 1829 MSK1 kit.)
The extra tiles makes the game play more open and richer in choice of track building and upgrades. But play without these tiles is equally fine although the game can be a lot tighter and more critical with restricted numbers and choices of tiles. Both ways of play are equally good and could be just a question of the flavour of game you prefer to play.
To me, it makes more sense to have one supplementary tile set for 1825 rather than two, and this brings the available tiles much more into line with what an 1830 player would expect. Some interesting options, Tile 174 is just genius!