Who did you order from?
How much were you looking at?
ETS now I think, all the same with P markings on the mid boxes
"P" aka Polmo are trademarks of POLMOstrów, which is a Polish exhaust manufacturer.
It seems that exhausts for Omegas are becoming scarce and the prices are rising.
You
could try here for Kit 350 for a 2.5 saloon. This company was selling the Polmo exhausts on ebay UK but stopped post Brexit. However I understand another member managed to buy a kit directly some months ago. Certainly the website implies they will ship to the UK. AIUI import duty is only charged on goods worth more than £135 and import VAT on items more than £39. So you might be liable for VAT on import plus the clearance fee, whatever that is. Lot easier if you buy something already in this country.
I ordered one from auspuffteile via ebay several years ago and the kit arrived from Germany in about 5 days. The product was Polmo and the quality and fit were fine. Way better than Bosal.
One problem is that the exhaust suppliers are now shipping the Omega centre boxes, presumably for other makes as well, with a cut in the downstream pipes to the back box. So each centre box is in two sections joined with a sleeve. This presumably to shorten the shipping package and save some cost and/or storage space. At first sight this doesn't seem to be an issue but in fact it makes it a lot more fiddly to fit as you have to get everything lined up exactly in-situ before you seal and tighten. It's harder to do if you have no ramp or a pit. The Eternal exhausts are now supplied cut. And I suspect the Polmo ones are as well, no matter where they come from.
You can also use a 3.0L saloon exhaust, the difference is the back box has twin tailpipes instead of the bigger single tailpipe on the 2.5L. Kit 351 is for a 3.0 saloon, I believe.