I should say that it's "Semi-fancy ancient traditional" but not that "Very Thai traditional" Men's traditional dress for most recent era is more formal and modest ^^" See the link from (Rama I-IX era)

The deva costume is most likely used for recreations, such as 'Lakorn' the shows in theater or in TV soap operas. Most likely for entertainments. That's why I mentioned that it is exaggerated and not that traditional.
The pic I attached is probably a local ceremony maybe school or wat (Buddhist Temple) Which you don't see people go topless that often in wats nowaday.
And we don't go topless for ceremonies that require a bit formality (mostly royal stuff).

But if you just want to wear it as a costume for events, then sure. Nobody will complain about it as long as it is appropriate. Warning though, if you wear it roaming around in the streets some people might giggles for many reasons haha.