The amount of light that the Swarovski EL TA Range let in is amazing. This is my first pair of Swarvoski binoculars and I really am impressed! I can see in the dark well before sunrise and well after sunset. Not really a huge need for the TA (track assist) IMO?
I have never heard of GPO but did a little researching and they have really good light transmission as well looks like 92% and the price is half of Swarvoski.