I have a stackable washer/dryer unit that also uses gas for the dryer. Although I don’t own a condo, I’m assuming the reasons are the same - limited space.
Generally speaking, due to space considerations, these units are not extra-large capacity so you can expect to be doing more loads than with a side-by-side. Overall I have no problems with this but I’m a single guy and not handling laundry for an entire household.
One problem of course in anything that has an integrated design, if something goes wrong with the washer or dryer, you cannot replace the individual item. You are stuck either repairing it or replacing the entire unit. As always, it is a cost/benefit question. My unit is fairly old (maybe 1995 and was in the house when I bought it in 2006) and I suspect that when it needs repair I will be replacing it with a new unit. I have had to have one service call, a circuit/sensor thingie (technical term, you can look it up if you want) burned out. I think with the part and service call, it was just under $200. Anymore than that and I would have just bought a whole new unit.
Oh, mine is a Kenmore mumblesomethingsomething modelmumble