You are comparing chalk with cheese, there. DW = heavy duty, trade, accurate, well respected, long-lived, good spares availability for long time, etc. SIP, on the other hand..... DIY and a lot cheaper.
Basically all of the "big hitters" offer 230 volt versions of their 300mm/12in trade mitre saws, e.g DW, Bosch, Milwaukee, Hikoki (ex-Hitachi), Metabo and Makita. They all have pros and cons; for example the Milwaukee and one of the Bosch models (the one with the reticulating arms) are both massively heavy if you ever need to shift them, the Hikoki is not the most accurate saw out there, etc. Any trade rated saw will be more robust and accurate than a DIY model such as the SIP, but you will end up.paying for that.
My own more recent experience is with the DW, Makita and Milwaukee saws, hence my comments about weight above (I also have a colleague with the Bosch on the current job - he needs a mobile base to cart it round and it goes up to upper floors on the freight hoist rather than being carried), and whilst I am often "Mr. Makita" I'd choose the DWS780 over the LS1219 any day of the week on the grounds that the DW fence arrangement is somewhat better than that on the Mak and that the shadow line technology DW incorporate for cutting alignment is virtually foolproof unlike almost all the lasers on the market (the exception being the Festool Kapex). This is, however, a personal bias and I'd recommend going somewhere like an Axminster Power Tool shop, DW dealer, etc. or the like to get a hands on feel for any saw you are interested in as these are expensive purchases and you may just find that a 12in saw is just too big. After all, most tradesman do perfectly well with an 8in or 10in saw for most of their lives, so do you really need a 12in saw?
