The price for the s5 is $2100. The price for the alr5 is $1759. That's a $341 difference not $50. In any case, I considered the s5 but I bought the alr5.
The s5 uses 300 series carbon which is a low grade. The alr5 uses 300 series alpha aluminum which is their best. IMHO the price difference is not worth it.
BTW, the alr5 is a superb bike. I'm not disappointed one bit with mine.