I have a couple of trips (revenue bookings) lined up on S2 for the festive season and Jet-K has just sent me an email, stating that i could avail a confirmed upgrade to J for INR 2000 per-segment (~4.9% tax extra) (subject to availability- untill 2 hours prior to departure). It also states that I could process this online or on call.

How is this INR 2000 per-segment offer, different from the one offered at airport probably for much less..?