The extended grapple depends on which character you're facing and mainly the stage. If you're on FoD or YS, it can be really good and get you a lot of grabs. If you're on longer stages, or ones with high platforms, then it's not as useful.
Characters that rely on platforms or just have a lot of lag from aerials, such as Ganon, CF, and Marth, are really good to do it to if you're on a small stage.
In general though, there is no negative to the extended as long as you remember to do it at a time that doesn't leave you open and most importantly, remember that you have it. The time it's out is the same as the regular grapple, and if someone foolishly tries to spotdodge you can always get the grab. One tip is to make sure that you don't get anxious when it's time to press A and grab. Often you'll think you're close enough and try to go for it, and the opponent will spot dodge or jump or something, making you miss, but if you get in the habit of hesitating just a bit to see what they do, then you're sure to get the grab far more often.