I use a Domino 700 with a Seneca adapter and CMT bits. I also mostly use home made tenons. The CMT bits are about half the Festool price and work fine. You need the Seneca adapter to use the 6mm and smaller bits intended for the 500 on the 700. I've used it to make large slot mortises, up to 3 inches or so long - actually in one case significantly longer. I just plunge repeatedly to make the longer (I think more normal) mortises. I've made a crib with my 700, a queen sized bed, and a bunk bed. I also used it to make joints including drawer corners in a dresser. The drawer joints were fine but I will do carcase joints other ways in the future. The project is fine but it didn't locate the dividers as well as my normal shallow dados.
I also made mortise and tenon joints for years without a domino. A plunge router works well and can make mortises in both pieces so you can use the same sort of inserted tenons. I have a hollow chisel mortiser and it works. But the bit is difficult to get back out on the first cut and the mortises don't look as nice as a router or domino make. But they work fine. My point is just that you can do mortise and tenons very successfully other ways. But the domino is the fastest and easiest way to do them.
The project you mentioned that most indicates a domino is the table. It isn't super easy to make tenons on the ends of apron pieces. Best way I've found is with a dado cutter on my RAS then trimming with a shoulder plane. That works fine but takes MUCH more time than plunging a domino into the end grain of the apron. A router can also be plunged into the end grain but if the table is big, it isn't easy to get the piece vertical and cutting on an angle with a router isn't super fun - but very possible and I do it sometimes.
The biggest bit a 500 can use is a 8mm - about a third of an inch. The deepest it can plunge is about an inch. The 700 can use a 14mm cutter and plunge 2 3/4 inches. It's more money but I'm glad I got the XL.