Apparently El Al (LY) have also just announced a daily ex Sat Tel Aviv - Luton rotation with 763's. LTN is convenient for the very large Jewish community in north London. So maybe the MAN flights are part of a general route expansion by LY.
Yes, LY have very stringent security requirements.
Are TUI continuing with their MAN-TLV flights though? I have heard they are likely dropping LTN-TLV.