Best to max out the contributions and then sell as soon as you can, to invest in a fund elsewhere. Obviously depends a lot on the company, but any run of the mill firm, probably not worth eggs-in-one-basket.
I've not maxed out contributions, I've spread the contributions for the share scheme across each year of the three year cycle.
In regards of the PAYE scheme, I've maxed out the matching shares returns...
The company that I work for will be exist long after I die, "Too big to fail" springs to mind... lol
I just don't want to be hold 1000s of shares and be in situ where I have to pay management costs, if I don't sell them and it be a bad time to sell them.
Also asset allocation, captial gains taxes et al...