Using it in the modern way is fine, but generally a historian who knows about the era would use it very differently.

Anglo refers to the Angles, a peoples from the North Germanic plain, at least as far back as traceable, which inhabited parts of Eastern England.

To the South of them in England were settled kingdoms of the Saxons, a diaspora also from somewhere around the North Germanic plain (a lot of western europe is).

This initial rivalry perhaps was assisted by the fact that they were two people from largely the same place, who settled right next to each other.

But comically, in the end, their blended name came to represent Britain/its progeny diaspora.

At the time, though, they were relatively minor kingdoms among *many* in Britain.

The Saxons went on to found West Seaxe => Wessex which would go on to be the tribe to unite England.

But not before the island's population, culture and genetics were altered irrevocably by the many many diasporas there--Angles, Saxons, Britons, Gwynedd and Powys etc (Welsh), Strathclyde (Welsh in the north), Scots still residing in the northern islands (as the clan Dal Riata at the time), Celts, Jutes, and soon, the Danish (and Norwegian and Swedish, but mostly Danish) who would fundamentally shift all of Britain and even the world (suffixes like "burgh" as in Pittsburgh is just one example of the linguistic legacy of Scandinavia in the modern English language).

Edit to follow up: so, to clarify, an historian would be fine with its modern usage, but would more likely think first about the eventual kingdom that formed from the blended Angles/Saxon diaspora/rivalry, which would go on to form the aristocracy of England (for a while, at least).

Another edit, to give you further perspective on England's hegemony over the world for hundreds of years.

All of this was happening in Post-Roman Britain. Britain is an excellent island for a lot of reasons--geographically, farming-wise, tactically and more. So when the Romans left it was a hundreds-of-years long pretty much constant battle for power in the area, eventually leading to two blended tribes sort of "winning" for control in the end--but of course as always happens in history, Anglo-saxons are not particularly, to this day, the precise lineage of most Brits.

Even their aristocracy has been variously German, French-viking-derived ( Normans ), Scandinavian ( the North Sea Empire ), Welsh ( the Tudors ) and... well mostly German, haha. The current House of Windsor exemplifies this blended history, as it used to be the house of Saxe-Coburg and Gotha, from an area in Germany literally stilled called Saxony.

In the end, whoever controlled that island was likely to become powerful, as indeed did happen, very very much so. Hence the ubiquity of "Anglo-Saxon" and its continued relevance to this day.