Share Incentive Plans

I'm considering changing jobs and my new employer offers a Share Incentive Plan (a type of employee stock purchase plan). It seems like it would be a great idea to participate since I can buy company stock with pretax income and no UK tax will be charged on either the principal amount or the gains if I leave the shares in the plan for at least five years. It won't be pretax in the US but I can use up some of my excess foreign tax credits to pay the tax on the principal amount.

Has anyone ever participated in this type of scheme in the UK and do you think it is suitable for a USC?