There must be a reason why coffee bags haven't been part of normal life for the last 40 years, like tea bags have.
Coffee goes off pretty swiftly after it's ground, unless it's stored correctly. This is why ground coffee is vacuum-packed and should be stored in the fridge after you've opened the pack.
With teabag-a-like coffee bags, the only way they're going to be as good as "fresh" ground coffee is if each individual bag is vacuum-sealed, which I expect would be prohibitively expensive (a theory which would be borne out by these single-use cartridge system machines).
in Tesco a box of 18 is under £3 its 18bags individually sealed, they are a touch larger than tea bags and need at least 3mins brewing time.
for 18 bags at £3 its about 17p per cup which is comparable to a decent bag of coffee that you would would push thru a cafetiere using the same brewing principle. its just more convenient and saves effort cleaning up afterwards.