I have owned both and this time I ordered the vented separates from the factory. I also ordered full body paint and was pleased to have the vent located, installed and painted as part of the paintjob.
For me, there are several problems with the combo units. First, they seem slow and take "forever" to do one cycle. Second, you obviously have to wait for the washer to finish before you can start the dryer. If you have a larger load build up, you'll end up doing laundry every day for awhile to get caught up. Lastly, the non-vent combos "condense" in order to dry. In my ventless unit, the "dried" clothes always came out damp & wrinkled.
Having owned both, I think the only way to go is to order the separate pair (if your model can fit both like an RL/RE/BR) and have the factory install them. If you want them, just get it over with as there is definitely no savings in an aftermarket retrofit. Plus, you have to remove the bottom of the W/D closet and install the pans yourself even with the factory W/D "prep".
Mike & Pam '12 36RL, Kodiak Discs, 17.5" G114s H-Rated, SRE4000 w/HD Shackles, Joy Rider Shocks, Flex Air, 5.5 Onan, W&D, DW, 4 Scare Lights, (2) 6V Trojan T-145s; Progressive EMS-HW50C, Winegard DTV Sat, Sony/Denon 4K Home Theater, WiFiRanger EliteAC Pack, weBoost 4G-X Cell Booster.
2020 RAM 3500 Limited CC, LB, 4x4, DRW, Cummins HO, AISIN, 4.10, Curt A30 w/OEM Prep, Transfer Flow 70gal Aux Tank/Toolbox.