28k outside of london is good. If they are getting funding then they are probably also scaling up, you want to get on the leading edge of that if you can. Career wise that might be worth more than equity.

Equity is a double edged sword, sure you get extra value but you are also tied to the company. When things are going great you don't want to leave and when things do sour then you cant because you just lost money and may feel a moral pressure.

28k is also a good figure as it will springboard you into all kinds of other job roles (because recruiters only look at previous salary). my salary jumps were similar in the beginning.