Is use of the ® symbol to be recommended?
In principle, yes, but use must be in keeping with the facts, i.e. where geographically the trademark is used in conjunction with the ® symbol a corresponding trademark registration must have been obtained.

Use of the ® symbol must correspond to reality and be true from all points of view.

If for example the ® symbol was used in conjunction with a trademark on a product not covered by a formal trademark registration or if the trademark with the ® symbol was used on products or advertisements in a jurisdiction where no registered trademark has been obtained, this might have undesired legal consequences.