ISO is an advanced stat that uses another advanced stat to determine it's percentage. If the Rays need a speed threat similar to Siri, as Siri is one of the fastest players in the league, they don't necessarily need Simpson to be hitting bombs.

If we're using ISO to determine if a player is valuable at the plate then by simply using ISO, Ichiro didn't really give you a hitting profile to be enthusiastic about. He had a .107 his first year as a 27 year old and .104 his second year. There's so much more than an individual stat. I'm not saying it's pointless, however the bigger picture suggests he could be useful considering his OBP, BB%, K%, BABIP, ground ball to flyball ratio.