Well I have a 60w Klipp and a 100w Klipp arriving VERY shortly so I guess I can give you my opinion. ;)
Klipps were made between 1970 and 1975 so yes, they're old. The overall tone is best described as a clearer, bassier Marshall Plexi/JMP. The clean channel is old school - crank it up to get the gain working. You would need an attenuator or a pedal to get low volume crunch and overdrive.
The Klipp channel is like a built in Fuzz pedal, giving a grainy and loose tone. It does a great "Iron Man". However, the Klipp channel tone is an acquired taste and isn't a classic "Thin Lizzy 70s Rock" type tone.
Basically, if you want to use the amp's gain then a Klipp is no good for shredding without additional help via a pedal. It's a proper "old school" amp.