Agree with vivamuci
I was able to get J award ticket OW TLL-IST-LHR for 12,500 miles and €87 tax (not much less for Y though), which in my opinion is very good value, considering revenue ticket costs €700+. Y redemption is definitely not good value.
I guess intro-Europe taxes are lower, though using TLV or AMM as starting point you only pay €40 extra in tax and same amount of miles.
And it's relatively easy to accumulate miles on TK's M&S, as you get the exact number of miles as you have flown on TK metal, whether discounted or not. In comparison the LH M&M is useless...