If you are going to be using an SLR, and want to take photos when the light is fading, of the stars, or at slow shutter speeds (less that 1/60th) then you are most likely going to be needing a tripod.
It is easy enough to pop into somewhere like argos and buy a cheap and cheerful tripod, but you will be dissapointed, and then go and buy a decent tripod anyway! So why not save the time, money and dissapointment and get something that will do what you need from the start.
The sherpa 550R certainly does it's job, keeping your gear steady for taking those slow shots, and will allow you to use a reasonable telephoto lens too and hold it all nice and firm. I have been using my 70-200 f2.8 perfectly well, and also wide angle shots of the stars with long exposures. With the centre column put away this tripod is nicely stable. When fully extended there is a little bit of movement, but nothing too drastic. A useful function of this tripod is that you can adjust the angle of the legs, this is useful for stradling obstacles, and providing extra stability. The centre column also splits in two so you can get extra low down too, ideal for photographing flowers and the like.
A head is included with this tripod, which saves a lot of bother, and it is a perfectly good head too, requiring just one turn to move it about, and one turn to lock it tight again. Of course you can replace this head if you want to have a bit more versatility with a ball head or panoramic head, but I've not felt the need to.
Well built from aluminium this isn't the lightest tripod but this can be a blessing as it makes it more sturdy and robust too. I wouldn't say it was overly heavy, and I am quite happy carrying it about with me when I'm out.
For this price you can't expect miracles, sticking a big 500mm f4.5 is obviously not going to be ideal, but if you have big glass like this then you should be spending twice as much on a sturdier tripod.