I don't have the adjustable model but I quite a few other models hoarded over the years. Generally the mains heater is bullet proof, the tips are well made, good plating, wets easily. Not so when it over heats itself, I use them when I need a second iron when desoldering thru hole two leaded parts ie, capacitors. If you are in the UK, then Antex is no brainer.
Tips: get some Ceramic based Anti Seize to go between the heater and the tips. This prevents binding and helps with removal. My Antex are all clamp style tips it was hard to remove until I applied anti seize. I use it on my car brakes caliper guide pins.
Don't use Copper anti seize they are no good for Stainless Steel, the Antex heater might be stainless steel. Nickel Anti Seize is okay but it is reported to be carcinogen. I think as long as you apply it thin and keep it away from the handle it should be alright. Hakko users can try Copper Anti seize, since the connection is between ceramic heater and copper tips. It might improve thermal coupling. Don't use grease, they don't last under high temperature.
http://www.amazon.com/Permatex-24125-Ceramic-Extreme-Lubricant/dp/B0018PSASUWhen I was a kid I worked at a Sharp factory manufacturing cassette players. The Hakkos ran 8 hours a day, the barrel charred, burned marks all over the stand. The tips lasted very long. This
was before lead free. I believe lead-free temperatures kill tips. You don't need sleep function for a long lasting tip, keep the working temperature as low as possible that is enough.