I must say that the field kit to me is a bit of a mixed bag. It’s very cool, but you need to be aware about what it isn’t and what it’s missing somehow.
It sometimes feels a bit like some of its functionality is only half there and needs a modular to really work at its fullest. For example the solenoid interface is much more interesting with a sequencer, and the motor also is more interesting with some more advanced modulation. Also, it’s not as field-proof though it kinda runs on a 9V battery (with limited functionality)… but check the field kit topic here for more info.
This said, the DC interface is one way to control a tape recorder’s motor and the 4-channel contact-mic-proof mixer is great and you also get a radio, with AM! So it’s still worth it imho. Justy keep in mind that you’ll want to put it inside the modular at one point 