Hello,
I have the AF 48-1. Just to clarify, Metz is a bit confusing when they talk about the slave capabilities of this flash, so yes, sometimes it uses the term SERVO instead of SLAVE.
About remote controlling this flash. As 'Eire69' pointed you can only fire this flash in remote mode with another P-TTL flash. I can fire mine with my K5's built-in flash, but also (surprisingly) with my Godox AD200 in PTTL mode. Anyway you need PTTL mode (the Metz needs to detect the pre-flash).
After the (I think) v4.0 firmware version, you can program your Metz so, in slave mode, you can set power manually. That is, you still need a master PTTL flash to trigger the Metz but you can set the power from 1/128 to 1/1, in full EV steps.
Maybe still a bit limited (it needs to detect a preflash), but can be done. About how to set SLAVE/SERVO mode, you can chek here:
Enabling "Servo" mode on Metz 48 AF-1....: Pentax SLR Talk Forum: Digital Photography Review
The metz's photocell is not very sensitive, you need to point your main flash so the light can reach it, so your main light needs to be at right side, and the Metz flash at left side, to avoid misfires.
If you need a really dumb slave mode, without preflash, then it's better to search for a external photocell or a cheap pair of radio trigger/receiver.
Regards.