I would go for it. It is basically Weekly Alicorn with 40 energy every time. Alicorn is 600 gems...Unicorns are currently 250....
I have passed up some good Alicorn offers in past...but now I jsut went for it and bought 3 Sweetheart Unicorns ( already had one) - NOT A SINGLE REGRET. In long run, much better. And well - I rather bay it on something useful, than accidentally speed up some Dragon