The things that concern me about ordering online are 1) Not all lenses are of equal quality; 2) Better opticians suggest staying with a lens maker/model that works for the individual, since our eyes handle some makers and models better than others; in my case, that's been Varilux Comfort (prgressive), which doesn't seem available online; 3) Being able to go in and know the shop will provide adjustments and sit and work on fit, etc., which is  needed a couple of times a year, and do it w/o hassle because you bought the glasses there is not a small thing.

Progressive lenses are hard to buy online. Apparently the measurements to fit the lens to the center of your eye is different for near and far vision. But it's easy to visit a brick and mortar optometrist and pay $15 for an adjustment of any pair of glasses.