As far as I know there's two DLC packs going for about 5 euro. To me this sounds rather pricey for DLC so I just wanted to know, what can I expect from them and how long are they?

" This looks like it has a bunch of info. Hopefully that'll do it for you. "

 Interestingly how much you get out of the DLC time-wise may be inversely proportional to how much you get out of it fun-wise. That is to say, the content itself is fairly short, so if you're getting tons of hours out of it, it's probably cause you're dying alot. For most, the new missions are probably the bigger draw, but they're the shortest part  of the DLC. Edy's mission is not just extremely short, but also somewhat frustrating. Selvaria's mission pack offers alot more, both in gameplay and in story/character, but ends right when you start getting drawn in
 
The Hard EX mode is exactly what it says on the label and it lives up to its name - if you're all about a tactical challenge the extra hard skirmishes offer up alot of fun new gameplay. If you didn't really care about skirmishes, and don't care about pushing your tactics to the extreme, this content isn't for you. It would have been great if they allowed you to replay the story missions in Hard EX, but alas. As such, there's nothing really "new" here,but the increased difficulty and lack of tank makes you approach the old skirmishes from a totally new perspective, so if you replay all the skirmishes, that's a decent amount of game time to sink in. I personally think bumping the challenge up to extreme can occasionally expose the flaws of the dice-rollin' RPG under-the-hood mechanics, as sometimes missions will come down to random chance- like whether or not you or the enemy manages to auto-dodge, activate potentials, or land hits and headshots.
 
If I had to recommend just one of the DLC packs, I'd go for the Selvaria missions. That being said, if you're just a big fan of the game and like some challenge, you'll probably at least ENJOY them all, but might be a bit miffed at the shortness of the missions and lack of true "new" content.