Good value & good quality prints

I have used Pixum several times to print out my entries for my Camera Club competitions. Generally speaking I am pleased with the results and will continue to use them. The blacks are particularly well rendered and I have had compliments from judges in Black and White competitions when it has been noted that my prints were amongst the few with 'true black' colouration. However, I do find that some prints lack the saturation of colour that you see on screen. I also find it very frustrating that Pixum crop the actual print to the size of the image. To my mind, if I order a certain size, I should get a piece of paper of that size with a white border around my image. If, for instance, my print is in letterbox format I would still expect the full size of paper with a big border top and bottom. When the print is cut to the actual size of the image it does not allow any margin for mounting.