trueSpace 7.6 (dunno about previous 7.x versions) only has glue as sibling. Will that be a show stopper for using 7.6 for Freespace modeling?
The explanation for removing it is in the manual's Appendix.
A.1 Avoid Complex Hierarchies
A.1.1 Replace Glue as Child links with Glue as Sibling links in older models
Glue as Child is functionally equivalent to Glue as Sibling, but it tends to create much deeper hierarchies. Deep hierarchies kill performance in all versions of trueSpace, so we removed Glue as Child from trueSpace altogether. If you have some models created in an older version of trueSpace that have a lot of Glue as Child links, you can improve performance significantly by ungluing them and converting them to Glue as Sibling links.