I had vague memories of seeing this show as a kid in the 70s, and recently found one of the Fanderson DVDs on ebay to add to my Gerry Anderson collection.
Well, let's be blunt about this: it's not very good. The effects and models are very much influenced by 'Space 1999' (the main ship looks a lot like the 'Ultra Probe' from that show), and for the era they're not bad. But the plot, characterisation and acting is even below 'Space 1999' levels and in many ways the setting makes even less sense. The music is also rather naff: the music in most of Anderson's shows was memorable in itself, but this one sounds like they accidentally used a music tape from a 70s cop show.
So it's an odd combination of science lecture (relativistic red-shift, etc) and SF adventure for nine year olds. For me one of the the biggest issues is the way it makes the kids such a major part of the plot: I mean, are you really going to trust interstellar navigation to a ten year old boy? They justify having them on the ship by saying that the adults don't want to leave their kids behind because they'll be decades older by the time their parents come back, both due to travel time and time dilation, but an adult crew might have made the story more believable. Another issue is that they lecture about relativity so much but don't understand it, nor is the technology even remotely accurate: an Anderson 'hard SF' show in the 70s would have been a pretty interesting concept, but you don't get that here.
All in all, an interesting curio and it might have made a decent series if they'd produced any more, but it's well below the standard of Anderson's earlier SF shows. I couldn't recommend it to anyone other than Anderson fans, but if you do want to see it the Fanderson DVD has both NTSC and PAL versions on one disk and decent picture quality, so it's probably the best way of doing so.