Iirc, in the LN, the summoner class can only use one summon at a time, so the time-stop summon just buys time. Because he can use multiple classes' skills, it allows him to spam magic for those 3 minutes.
Even without the box-standard of classification, I would not classify these as safe given the existence of other SCP. They are shown to temporarily disable an individual's desire to capture them. Presumably, this means that capturing and containing something against its will is considered...
@Mahdii
In that case, I'm not sure what to make of the flowers on pages 25-26. They are dyed black, which could just be the same blood that the large flower is covered in. However, they are also withered and broken. Maybe the large flower chokes them out when it blooms or the brother trampled...
Elaina's behaviour is consistent with the first chapter. At that time, her identification went missing and she waited days to get it back despite knowing where it was. In this case, she waited a day because she assumed there was no immediate threat. It seems like she burnt the field of flowers...