I found out that some potted plants have more individual plants than those sold in bundles. I've bought crypts in pots that always have roughly 8-10 small individual plants. I've also bought them in bundles on a few occasions and usually only receive 4-5 plants per bundle. I'm almost sure the lfs owner where I got my crypts last week got a $6.99 pot and made 2 separate $6 bundles.
I generally prefer to buy bare-root because I can see the roots, and I don't have to deal with removing rock wool, which has to be done slowly and carefully to avoid damaging roots. (Tweezers, toothpicks and a bucket of fresh dechlorinated water are essential for that messy job.) Some people do use potted plants specifically for quarantine tanks, discus tanks, goldfish tanks, or other specific set-ups, but I'd guess most PlantedTank folk like to depot and plant.
I've found potted plants, especially ones that have been in store for a while to be the best bang for your buck. Pretty much every crypt, sword or dwarf sag I've gotten from a pot has had multiple sprouts coming out of the root system. One time i separated a pot of $4 unidentified crypt into 8 individual plants and all did well.
In regards to wanting to see the roots, most of the time you can judge a root system by looking at the lushness and pretense of new growth, and the fact the almost all pots have a million mini roots bursting out of them..