The Free Presbyterian Church of Ulster (which also has the sister church in the US, the Free Presbyterian Church of North America) is most closely associated with Ian Paisley, the well-known churchman and politician in Northern Ireland who was not without controversy in the broader world. That being said, he is a sound, evangelical preacher. The denomination is known for being fundamentalist in orientation, being against drinking alcohol and in general emphasizing separation from the world. They also are KJV-onlyists of some stripe. They allow credo-baptist and paedo-baptist views on baptism and are not strict on the regulative principle or some other more traditional Reformed distinctives. I've heard for example of churches in this group using altar calls, and many have choirs, and I think all of them use instruments and hymns in worship. They also have a long association with Bob Jones University in Greenville, SC.
It's hard to find overlap with the Free Church of Scotland (Continuing) except that both are conservative, Presbyterian denominations based in the UK. I would say the biggest similarities are they both use the KJV (though the FCoS(C) also allows the NKJV and maybe some other versions, being more concerned about the underlying text), they both tend to emphasize experimental preaching, and both have a large emphasis on holiness (though I wouldn't call the FCoS(C) fundamentalist in orientation). Most FPCoU/NA congregations use hymns, often including revival hymns, and not a lot of Psalms. The FCoS(C) is all psalms and all a capella.