Had 2nd DE shave last night, better results, however my neck gets very irritated with a rash. Is that just getting used to it, bad technique, blade issue(derby), sensitive skin or a combo of all 3?
No, usually it does not irritate skin if you get your technique and set up right.
These are the possibilities:
1) Blunt blade. (Derby is a hit or miss blade so adjust your angle when you shave)
Some blades are better suited for some particular DE razors.
2. Angle of shave.
Make sure you play with the angle so that you cut rather than scrub.
3. Pressure.
Do not put pressure while shaving. Very little yes but not more as you will get razor burn.
4. Post shave application – cheap aftershave balm like Nivea Sensitive non-alcohol or whatever you have been using.