It is worth going for the companion voucher if you want to travel in club or first and want to go anywhere in Europe, but probably not if you want to fly in economy.

I just hit my 2-4-1 voucher this morning and looked at the cost of flying from IAD to MAN at Christmas (I live in DC but am from Manchester and we go back to visit the family for the holidays every year).

To fly in Club or First, it will cost us 100k or 150k miles and the fees are $912 each for either. To fly in cattle class it would cost 50k miles plus around $600, which is not much less than just paying for a cheap economy seat.

You can connect to pretty much anywhere in Europe through LHR as part of your redemption, but you just have to make sure that it is BA metal for the TA and the Euro flight when you are planning your trip.