I haven't but was going to get some to try. Parex wants more to delivery it than itcosts so I am going to give it a miss. Parex reckons it only re***ds the 'open' time not the initial set so it might not be worth it.
Found an alternative used in the concrete industry but got to trial it yet. Lot cheaper than Parex and goes further.
You'll struggle to get it here as its not designed to be used in temps below 20c it modifies the cements hydration in mono, concrete etc.
It's designed for warmer climates, but for the record it's around 40 quid a tub 20 litres if I recall, from there list.