It’s true that SPU’s as a ‘species’ have a certain ‘gestalt’ that can be easily recognised. But that doesn’t mean all SPU’s are created equal, far from it.
So this question depends on what SPU you are referring to. The SPU Classic with spherical stylus is loved for the musical rendition of the midrange, but the top and the bottom of the frequency range are missing in action. This could also be said of Denon DL 103, so there is some resemblance as both are ancient designs and that’s exactly how they sound.
Thankfully Ortofon has retained the basic design elements and their sonic strengths for more modern versions that do not suffer from the limitations of the original. I haven’t heard them all, but the ones I do know very well - SPU Gold Reference and the A85, A90 and A95 Anniversary models - occupy a very different sonic (and financial) universe. There are significant differences between them, but each in their own way manages to amalgamate the musicality of the original with the full frequency extension and transparency of more modern designs, so as to ‘have your cake and eat it’.
The only similarity between these more modern SPU’s and Denon DL103 is that they both require a heavy gun as a tonearm. There are people who seem to think that the 103 is all they need and are fairly loud in attempting to convince others as well. Obviously they’re free to believe whatever they like, just don’t take their word for it and listen for yourself. The used market is absolutely riddled with 103’s (just check hifi shark) so you can try one without any financial risk. If you don’t like it you can resell it just as quickly. I know I did!