ATK X1SE vs ATK X1S?

I posted a while back asking for mouse recs, I am now leaning towards ATK X1 series (also looking at A9). But I am confused between the X1S and X1SE variants since I am not aware of what difference different sensors etc would make. Would it be wise to save some money with SE or just get the S for long term. I plan to use it for work mostly with some rare casual FPS gaming.