My SSIV + ST80 package arrived two days ago. The cheap eyepieces are, in fact, cheap eyepieces, nor do the focuser + focal length improve the situation. Visual performance is decisively superior even with basic plossls. The diagonal is modest but at least functional, a fact demonstrated by supplying it with basic plossls. That eyepieces which constrain instrument performance are supplied with these "complete" packages is very dissatisfying, as the tube itself yields pleasing views with only a minimal upgrade of quality in the optical chain.
In fact my interest in the package was mostly the mount, not the tube. That said, after two nights with it, I may yet keep it, on this mount it works perfectly, zero vibration, decent ergonomics, easily transported, and with competent eyepieces the views improve dramatically.
I studied all the mounts in this class and the SSIV won for my use cases. Particularly the standard SLT does not provide fully manual motion nor as mentioned does it have optical encoders. For me this matters as I enjoy swinging the scope by hand and simultaneously desire freedom from electricity -- with this mount a get both, on a whim. The on-paper capacity rating of 13lbs is ~60% greater than the standard SLT and reports are it handles just fine compact scopes near and even beyond its limit, something I need as I fully intend to outfit it with a 127-150 cass in the coming weeks. I don't care too much about this, but the accessory tray is of higher quality and if nothing else, heavier and easier to outfit with additional center mass if required. A major issue is serendipitously finding this mount in the pre-owned market is very difficult, whereas the SLT is relatively easy. Lastly, the SSIV weighs more, hence unless one has actually stumbled across a pre-owned unit within reasonable driving distance, the fully burdened cost (i.e. with shipping) rapidly approaches a new unit which of course will have a warranty, something to consider with a motorized device the actual usage profile of which is unknown.
All that considered, I went for the package and do not mind the extra hundred dollars or so since I get a new tube along with it.