Its easy to mix but I don't use over 3L in 8 months. It keeps 2x longer in a 1/2 filled container vs D-76 (2 months shelf life).
One more time here, you can buy a case of 500mL amber bottles from USplastic.com for about $25. Decant your 5L of XTOL into ten bottles and you will always have super fresh developer. My last batch stretched out over 1 year and was perfectly fine. It's a very worthwhile investment if you're into XTOL.