Do you recommend always wearing a Mandala as a support even if you are only going to use a Mandala that you just bought?
Or can it affect the new field by having more than one Mandala?
No, the effect will not be diminished. Mandalas can be combined freely, and you can use multiple ones at the same time. They do not interfere with each other.
@Maitreya While using the protection fields will the attacker gets harmed or it only guards only me and here I am saying most of the protection fields except return to sender field.
It can be harmed by the Helm of Awe and Return to Sender. Chameleon protection can bring him into illusion. Christ field, can make him or his demons very angry, but the reaction will be to run away from you, not attack.