Oh man I remember those. My father was an electrician and got me started when I was 15 and dropped out of school to work when he was injured. Not many of them to work on then but we did run into a few in old Galveston. I was glad when the word came that we had to start switching them out whenever we worked on one.
I just finished wiring up two ceiling fans in parallel in the shop, and I used these Wago three-way connectors. They really are convenient compared to the twist-on caps, but you do need to be careful not to pull too hard on the wires, as they can come out of the connectors. Stranded wire seems to stay put more firmly than solid wire.
To me they was harder to get back off the wire if you had to unwire a connection and have had a few to not make a good connection and would loose contact and would have to go back and rewire, but like i said have only used a few so it just might be me but have used thousands of the twist on wire nut with no problems.