The Sealines are pretty solid reels, but what is this Interline? You said it's a daiwa combo so I'm assuming it's some Daiwa rod. Sounds pretty cheez. Big 5 combos are not the way to go. There are very few companies that make rods equally well as they make reels. Penn- good reels, $hitty rods. Shimano- great reels, some decent rods. Daiwa- good reels, $hitty rods. Get the point? Normally companies specialize in either rods or reels, and don't put much effort into the other one (rod or reel, depending on what they specialize in). So, any combo you buy is sacrificing either the rod (usually) or the reel. Daiwa for instance makes pretty good reels, but their rods are $hit. If you're concerned with money, which I'm assuming you are, buy a corsair and a cheap all star, lamiglas, calstar or seeker or something. Don't skimp on the rod, it's tougher to get a rod fixed or replaced than it is to get a reel fixed or replaced. Cheap rods are also usually more easily broken than reels. You break that Daiwa rod in half, bummer, you get to buy a new one. You break that Daiwa reel, learn how to fix it, or take it to a tackle shop, 15 bucks, back in business. What are you using this setup for? Pier fishing? You asked if Sealines can cast- uh, yes they can. I'm a little confused about that question, but yes they can cast. If you only need a pier setup, go for the cheap stuff, you're not going to be putting much stress on it anyway. If you're going to get serious and fish it on party boats, or buy yourself a float tube, or something like that, you'll catch bigger fish and use it for more applications and will thus need a higher quality rod, but for mackerel fishing off the pier, it doesn't matter.
-Brian