Any question answered...

Further to this, could I then plug it into a dictaphone or something similar for portability and being able to have it off camera?

Would the recorder bottleneck a good microphone or is a sound file just a sound file?

It should work in the dictaphone but in the same way that headphones sound completely different depending on what you plug them into there may be impedence discrepancy and a small cheap dictaphone maybe lacking in the power used in the preamp to get the best out of it.

These sorts of mic's were orginally used on those big semi-pro camcorders. But dslr is so popular now, that they market them directly at dslr's now and have redesigned the suspension bracket to be less fiddly.

I used to use a full size audio technica stereo video mic plugged into a minidisc recorder, and this was perfect for field recording. It was the "done" thing, I saw professional media people doing the same thing. The quality was superb. But now they make convenient all in one units like this;

zoom h1
http://www.dv247.com/studio-equipment/zoom-h1-portable-digital-recorder--73416

Here is a comparison;
http://www.learningdslrvideo.com/zoom-h1-vs-videomic/