Oh, they are legit and are mostly sold exclusively in Speedy Video retails store. Speedy Video have been appointed by Tsuburaya Production as an official licensing agent for Ultraman Mebius in both Malaysia and Singapore - distributed by Movie Master(most likely own by Speedy) in Malaysia, and by HVN(100% own by Speedy) in Singapore.
This is their official ultraman website, which remain unchanged since the announcement.
I don't have the one you linked since I've already got the japanese collector boxset, but I got the Ultra Galaxy Daikaiju Battle DVD volumes which were released by Speedy last year. - The dubs are horrible indeed, lifeless and bland. The quality for subs themselves ranged from somewhat acceptable to well good; they are pretty inconsistent, depending on the volumes.
Anyway, the english dubs and subs are made to cater the Singapore market, but Ultraman or any toku series are never really taken seriously in either Singapore or Malaysia. - "It's kids stuff, kids just watch it for the fun, there is not need for quality, all their parent's money belong to us" kind of mentality.
Here some pictures I took of the Ultra Galaxy DVDs. - they come with slipcases.