Physical albums sell well at shows because people want a physical souvenir. I’ve looked into dozens of technologies to replace physical albums, and finally found one that works. SD cards and USB sticks are cost-prohibitive – but dropcards are not. Dropcards are credit-card sized thick plastic imprinted with unique download codes that cost between 25 and 50 cents a piece (depending on the size of your order) and are much easier to carry than CDs. You can design them however you’d like, they can hold video and images, and people still get a tangible souvenir. Also, you’re able to collect the email addresses of those downloading the album. I’ve started selling them at shows and I’m back up to the same pace I was for albums a decade ago. I reached out to the people at DropCards.com and got a discount code for all Pro-Tip readers. Enter comedyprotips at checkout (we don’t make anything on the referrals, but you save 10%).
And re: track length, "The sweet spot of track length is two to four minutes."