True. Originally was using the 4x9 17220 case Ultraflo’s but the welds cracked at the lengthwise seams on a total of three mufflers (replaced the first set that both cracked under warranty) but one of the replacement set cracked agin (likely due to the harmonics/vibration and the way I have them mounted IDK) so I went with the round. No issues anymore. I got mine from Rock Auto and got the extra %5 discount as well. About the cheapest I found (3” in/3” out version)