that Valved Exhausts company is legit. i have had one of their titanium systems for 8 months now, and have had no issues with check engine light or anything. the one real issue i have with mine is the clamps loosen when they get hot, causing the alignment to get thrown off, but i contacted them about that and they said that since my purchase, they have updated the clamps to be much better. it took about a month to get my titanium exhaust, and the sound profile is very GT500-like. i was also able to verify the system was actual titanium with my dremel. the sparks were white in multiple places, which means its real. i have an issue with squeaking, but apparently that is due to buildup on the valves, so cleaning them every now and then may be needed. installing it was also fairly easy; when i installed mine there was a bit of guessing as to orientation of the mid and connecting pipes, but their support says that labels have been added since my purchase. and speaking of support, their support team is totally on it. very, very quick responses always.
overall, while they may look a little sketchy due to price, Valved Exhausts is a legit seller of titanium exhausts, and i recommend them for anyone searching for one