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I’m afraid I cannot provide any opinions on this one way or another, being as I am in exactly the same position as you. Funnily enough I was planning to make a similar query to your own shortly. One of my concerns was that I would assume that such a route makes the CPL skills test more difficult, since I would presume it would also include elements exclusive to twin operations i.e. asymmetric flight and as a result may lead to a need for even more additional CPL training than would normally be anticipated.
There is also the possibility that you will be more likely to fail the test as a result I assume. You hear a lot of talk on these pages about the need for modular guys to maintain a record of first time passes in flight tests and if there is truth in this (which makes sense) then it might be preferential to “protect the downside” and make things as simple for yourself as possible.
That said it does seem like common sense to roll the 2 into one from a financial point of view.
I would also be interested in hearing others opinions on this. The only remark I found unusual in your post was your understanding that most people chose option 1. I would have thought far more people actually go for option 2, but perhaps I am wrong.