orange coloured shoots coming from apple tree union

[FB.]

....still a bit confused as to whether or not to prune the shoots, would I need to put arbrex paste on the cuts ??

If you start messing with burrknots that are trying to root you could allow a lethal infection to enter the tree - this time of year canker and phytopthora thrive so there could be a lot of disease around looking for 'wounds' to infect.
The burrknots will give up trying to grow due to the air having no water, no nutrients and they won't like daylight. Eventually they will gradually wither away and fall off in the next year or two.

[FB.]

....FB may have a different opinion.

I agree with you. But even if I didn't, it doesn't mean we're not both right, wrong or partially right.

...I've seen some thoughts that the burr will girdle the tree but I doubt hacking them out will be of much use unless you get the lot.

Some new experimental rootstocks have sometimes girdled themselves with burrknots but the more well-known rootstocks (M27, M9, M26, MM106, MM111 and M25) are very unlikely to girdle themselves.

I've never seen one of the well-known rootstocks girdled from the burrknots, but I have seen them girdled if the burrknots get infected by canker or crown rot (phytopthora).

I've often used the phrase 'hit below the belt' to refer to a super-disease-resistant apple variety that died because its less-resistant rootstock became infected, usually through wounds (including strimmer wounds) or burrknots.