Tortex is Dunlop's twist on a material originally developed by DuPont and called 'Delrin'. Tortex has a somewhat tacky feel making them very easy to hang on to even with sweaty fingertips. Another strong point is their durability. No matter how much abuse, Tortex picks seem to last forever.
Tone wise the .88mm has a bright overall sound and a sharp attack. This has always been one of my favorite picks for playing rhythm on an acoustic guitar. It's a very controllable pick, able to handle everything from quiet and light to bash-fests without ever sounding to slappy or bashy.
For any guitarist starting out or someone just wanting a solid baseline for evaluating other picks, guitars, amps, or whatever, the .88mm Dunlop Tortex is an excellent pick to always have on you.