I've never seen the attraction of the internal mech, all those exposed wires, something else to go wrong. The external mech is a closed cable all the way from the rotary control to the hub, and virtually service-free.
"Virtually." You're supposed to put some grease in the external clickbox every 500km but very few owners appear to know this and fewer to do it. I put in grease at 1000km, 600 miles, thereabouts, but what's in there always seems fresh, so I don't think it matters much. Anyway, it's a ten second operation, thumbscrew off, grease in, thumbscrew on, quick wipe.