They're no different to drive than an ordinary unit and semi-trailer and - due to the rear connection configuration - follow in the same path as one without the additional trailer. Six or eight-wheel rigid trucks with a two or three-axle trailer (known in the trade as "danglers") have been around for years and no-one has complained vociferously about them, AFAIK.
As with all multi-jointed road trains, the difficulty is in reversing them. Reversing an articulated vehicle is actually quite easy, once you get the idea, then the knack, plus powered steering has made things a lot easier than when I was in haulage for a living.
Reversing a "dangler" is a bit more difficult, because it's "double-jointed," which makes for a bit more planning and lateral thinking, but you could always drop it, turn round, re-hook and push it backwards with the towing vehicle.
Reversing the artic and trailer road train isn't impossible, but it is very difficult in comparison. Sometimes, the only way is not to attempt it at all, but to park up the second trailer, then re-hitch the unit to it after removing the front dolly axle set.
That's a lot of faffing about,
but with suitable planning and the end to slavishly following unreliable satnavs, I don't see much of a problem, TBH.
Ray