I think it is over the longer term - I use that and SPlititmining (details on my blog) http://www.ukbitcoinblog.com - you have to understand that LOW RISK=LOW PROFITS and HIGH RISK=HIGH PROFITS (or high losses!).

So it might look like a bad investment because the ROI is quite slow but proper mining makes money without effort. As you grow your account it starts getting very interesting, with SPlititmining I have auto invest turned on so it just builds up my mining pool - so in between growing the pool that I'm using I'm increasing it's profitability and reducing ROI.

Too add be VERY careful - there are a lot of sites out there that CLAIM to be mining pools but in fact they are simply scams (bit miner.io for instance).