Are shot timers good to have?

I saw a deal on a Pact 3 shot timer on /r/gundeals and was wondering if it's a good purchase for a newbie to have? Are shot timers useful for someone who plans on training in mostly indoor ranges and as a newbie, how can I train with them? Or should I put off the purchase until I get more training and experience? via /r/CCW http://bit.ly/2LJ0vfb