The only reason I would advocate spending twice as much on an integrated course vs modular would be if there was a job at the end of it, or at least a high % chance of a job. Otherwise I'd favour value for money and go for modular. (If you wanted to improve your chances of employment you can get CPL/IR in both airplanes AND helicopters for the price some people pay for an integrated airplane course!)
As for flight instruction, do a course if you want to be a flight instructor. Don't do it to get an airline job because there is plenty of anecdotal evidence to show that it could hinder you more than help.
Airlines (generally) want experienced type rated people (DEP/DEC) because the training burden is least. Failing that they'll take experienced non-type rated people (NTR) because they know how to operate as a crew and can do a ZFTT course. Lastly they will consider non-type rated people with no multi crew experience. Obviously some airlines take a lot more cadets than others.
Unlike the US, Australia etc, the UK do not place great value on single pilot hours and some would even consider people with a lot of single pilot experience harder to train because they might struggle with the multi crew concept. Don't get me wrong, there are people who can instruct for 1000 hours then get an airline job, but their chances of getting a multi crew job aren't necessarily increased by having those hours vs a 200 hour cadet, and some would say instructor hours might make it harder.