Kind of piggy backing onto what Hozzie said, if you don’t own any saws at all and are only buying one at the moment then a good skill saw (some places call it a circular saw) would be my first purchase. I have the sliding version of the Dewalt compound miter saw that you linked, and I love it. I’ve only ever used the compound bevel for trim, mainly crown. I’ve redone 3 decks so far this year, and I honestly use my Dewalt Skill Saw more than anything else. I use the miter saw for most angle cuts, but most cuts in deck work are straight cuts on deck boards and joist boards, and for those it’s much more efficient to do it with the skill saw using a carpenters square as a guide. It gets time consuming climbing down or walking over to your miter saw location for each cut on a deck board. Depending on the deck size, you can sometimes attach all your boards, chalk a line and use the skill saw to perfectly cut your hangover, which is the only way I’ve found to make them perfectly match.
If you do go with a full blown miter saw look into the sliding model and definitely get a good stand. Also, once you burn through the first blade for any of your saws look into the Diablo blades (red). I like everything about the Dewalt blades except the price, the Diablos are usually cheaper and as good if not better.