I am not currently using it with 5e.
I have used it in the past. The dice are pretty swingy - they tend to create characters whose stats are lackluster in comparison to, say, 4d6, drop lowest. This means, characters will tend to die more, unless you are generous with allowing player sto re-roll sets of stats. You can combat this by scalling the challenges to the PCs abilities, but why downplay the PCs, only to then also downplay the challenges? What's the point?
Also, the in-order part means that the player really only gets to choose class, in the sense that they choose the class the character will suck least in. They don't generally get to pick what they wanted to play, or what the party needed. It is pretty easy to end up with a party that doesn't have effective healing, or effective melee combat.
If you are okay with that - if a high turnover rate and a party that may not have all the bases covered are part of your intent for the game, then this works well. Over time, there is some tendency for characters with bad stats to die off, while those with good ones survive (at least, in cases where the whole party doesn't get killed because of a deficiency in the group). If you are looking for a little more competence and continuity from the start, you might want a different way to roll stats.
A good question might be - what are you hoping to get out of using 3d6, in order? What is your goal for that choice?