Unfortunately, just as World Traveller redemptions are generally a very poor use of Avios points, economy redemptions are generally a bad use of Skywards miles.
First, note that you cannot depart from Heathrow with this promotion. Gatwick, Manchester etc are OK.
Second, note that you must book a return ticket. Saver rewards cannot be booked as one-ways.
Full details can be found on the Emirates website here (log-in required).
I did a dummy booking from Manchester to Dubai for mid April. The flight came out as 22,500 miles plus £298 of taxes and charges.
Given that I saw cash tickets to Dubai being sold for £315 a few weeks ago, this is clearly not good value. However, over holiday periods you should get a better deal.
Seats must be booked by February 17th. Travel dates are April 13th to June 23rd.
What I would say is, if you have a Skywards redemption from Heathrow booked for this travel period, you should consider cancelling and rebooking. For the sake of taking a train up to Manchester or popping over to Gatwick and paying the cancellation fee, you will be getting a large chunk of miles back into your account.
The following destinations are excluded from the offer: London Heathrow, Shanghai, Guangzhou, Hong Kong, Delhi, Kolkata, Mumbai, Ahmedabad, Hyderabad, Chennai, Bengaluru, Kochi, Thiruvananthapuram, Calicut, Colombo, Washington, Boston, Chicago, Dallas, Seattle, San Francisco, Los Angeles, Toronto, Manila, Cairo, Jeddah, Medina, Riyadh, Istanbul, Lahore, Islamabad and Basra. I was looking forward to a short break in Basra too ….