Collecting some comments from above:
Joints correctly and skilfully made using proper materials appropriate for the application, are good joints. It matters not whether they are Wagos, screw terminals, inline crimps, crimped lugs on a stud, soldering or whatever, unless you have to meet a specific standard that is more prescriptive (e.g. for ATEX or MF situations). As Davesparks points out (and I regularly point out to anyone who will listen) a good electrician can make a sound joint with any suitable material. Making connections is one of the most fundamental skills an electrician can have, which used to be taught in great detail but now seems to have fallen by the wayside. But it is a skill, not just a list of do's and dont's like: 'Blue crimps are OK for RFC's.'
There are many bad / unsuitable materials and unskilled persons out there. The dodgy insulated crimps from the car shop, the guy who has good crimps but uses a duff crimp tool, the numpty who crimps them with pliers and his mate who uses stranded-only crimps on solid conductors. The regs don't call these out specifically, because there is the overall requirement for proper workmanship and materials which covers it.
Crimping, using good materials correctly installed, is reliable and secure. If a cable can be pulled out of a normal crimp without damaging / stretching the rest of the cable, it wasn't properly installed. If I crimp a ring to a 2.5mm² tri-rated, put the ring in the vice and pull, the cable rips apart leaving strands still stuck in the terminal. Any good connection will not add measurable resistance, otherwise if it carries more than a whiff of current, it will overheat. A connection that does not overheat is not however automatically to be considered a good one, as it might fail with time or movement in a way that it should not.
Additional insulation (and sometimes even basic insulation) is sometimes required to complete a joint or make it suitable for the installation conditions. Heatshrink of the right type is a versatile material for many kinds of joint. Applying insulation requires skill and knowledge to ensure that it is adequate, e.g. of the same strength and durability as cable insulation. Just putting any random kind of heatshrink over an uninsulated crimp is not in itself adequate.
Personally, I'm not too fussed about properly made inline joints with suitably robust insulation lying within trunking. If there are many joints, or the trunking is very busy, or there is a reason for them to be vulnerable, then a terminal box is needed. Bare blue butt crimps are not quite up to the mark.
Perhaps I should run a course. 'From blue butts to bellhangers in 10 easy lessons.'