Howdy,
They are OK, but can get finicky. I had one on my first tank, a 20g. It worked OK when I could keep it dialed in, but if anything changed, it would not skim well.
Also, it might be too big for a 5g. I had the medium sized one in my 20g, and it took up alot of the tank.
I hate to say it, but a seaclone might be good option. The only thing in the tank is the maxijet pump. It might be too tall, so check it out.
Good luck,
Scott.