Tbh after just seven months I would be inclined to leave it, because the reality is that there are no guarantees. No guarantees that the relationship will last, and no guarantees that she will stay as involved with your DC although that doesn’t mean that she isn’t all she is currently claiming to be iyswim.
I think that a lot of people want to meet the new partner with the addage that they want to see the person who will be spending time with their DC when actually a lot of it is less about the children and more about themselves. It’s perfectly understandable obviously but after seven months I’d imagine you may not get an accurate picture.
Remember they are currently in the honeymoon phase, and even more so given he left you for her. They need to be seen to be making it work. Obviously it’s possible that it might work out for them, but as with any relationship, there are no guarantees that it will after such a short period of time.
FWIW I met my ex’s partner after a similar period of time although she wasn’t an OW. At the time I liked her, had no qualms about my DC going on holiday with her, a holiday which ex had booked after just six weeks saying that it would be a lovely family holiday,
and thought that she seemed like a decent person.
She was there for ex, went to some events with him, supported him through some difficult times etc etc. But oh how things changed. A year in she stopped being too involved with the DC, stopped coming round to his, they eventually got engaged and she fell pregnant almost straight away, tried to force him to move to be with her rather than the other way around, but as soon as they moved in together the mention of my name was banned in their house, several years on she has cut off all of his family, she never goes to any family events, is completely un-involved with the DC, in fact the DC now refuse to go there because of her.
So my meeting her actually achieved nothing other than to think at the time she seemed like a decent person iyswim.
Now DC is old enough to arrange his own contact with ex and I have no reason to be in touch with her even if DC did have a relationship with her.