Any one order these from Train World before. A few weeks ago I received a packet of these, and these are the worst rail joiners I have seen. None of them fit my Atlas flex track, I can't get them pushed on. Maybe I just got a bad batch?
N Scale rail joiners are tough to get on at the best of times, I need a magnifier and use needle nose pliers to do it. People will jump up and down on me for this but try either Universal Rail Joiners or Peco Rail Joiners (code 55 obviously). I've used both and have rarely had an issue with any of them. what issues I have had have generally been me not lining them up properly for insertion.
Atlas gets most of its stuff made on the cheap in South Africa (at last report) so who knows what the quality is really like.
If memory serves me correctly, the universal rail joiners are compatible with both as the only difference is the height of the rail. These are what I use: