I have got Metal Mule one, investigated for several months (back then MTC did not produce 2in1 system) and I believe MM is the best price/quality one.
If you ca afford - go for Akrapovic the finest on the market.
Anyway the weight saving is HUGE. The whole MM 2 in 1 weighs almost the same as one of the OE pipes. Saves around 10 kilos. And one should not forget the power gain. The sound is wonderful with dB killer on, without it I do not know yet
Whatever you choose, do not forget to remove/block the AIS, there is a very good thread here somewhere.
Last but not least you can search ebay for used piece but now as the season is on it will be difficult task.
Good luck

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that is how i feel about my XTR
Mods so far:
Hyperpro front springs; Hyperpro rear shock spring; modified air box; LED tail light; LED indicators + new relay; YZ pegs; Lucas aluminum bar; brisk spark plug; snorkel removed; DNA stage 1; second hand DynoJet O2 mod; crash bars; front and rear steel braided brake lines; soft EBC brake pads; mitas 07 tyres, 2in1 Metal Mule exhaust, Blocked AIS, tall OEM screen, OTR bash plate