Not absolutely useless, but very nearly. The fact that you have TT presumably as a co-pilot will help you to appreciate that an offshore heli job would involve a few more years in the co-pilot seat, but won't count for anything when applying to the large heli operators for an offshore job.
The heli world is VERY separated from the FW world and even if you were to invest huge sums of money in a CPL(H), you would be at the back of a very long queue of hopefuls trying for a job. At the moment the offshore market in the UK is buoyant and recruiting, but in all likelihood by the time that you could be holding a new licence, the large operators would probably be laying off pilots in the next downturn.
If I were you, I'd persevere in the FW world, which is more likely to need more pilots world-wide in the long term.