I remembered seeing this a while back when today I found myself peeking at Metz flashes.

The 54 MZ-4(i) is from their older SCA series of flashes which require a separate adapter to work on each kind of camera. Sort of nice if you want to use one flash on multiple cameras from different manufacturers but otherwise kinda ehh.

Their newer lineup of flashes is what they call System Flash, each one is built to work with a particular camera brand. Assuming you want something nice and powerful take a look at the 58 AF-1 digital and 48 AF-1 digital.

This is to go on a Pentax camera, right? The 58 AF-1 is more expensive than even the highest level Pentax flash, the AF540FGZ. Generally people go for the 58 AF-1 in lieu of their camera manufacturer's top line flash. The 48 AF-1 is more like the second-best flashes from the camera companies.

For Pentax you would be looking at these prices (from B&H):

Metz 58 AF-1: $400
Pentax AF540FGZ: $319
Sigma EF-530 DG Super: $299
Metz 48 AF-1: $250
Pentax AF360FGZ: $219