Great question!
Star Reloaders should have the Star Machine Works San Diego, Calif. and Patent number stamped on the tool head. I have heard reports of some Star tool heads finding their way onto clones, and some clone tool heads with Star decals.
Phelps, Berdan, and a host of other companies copied Star's design. Many are reported to have used "inferior" manufacturing processes and to have taken their dimensions from worn/used Star parts. Manufacturing based on inaccurate original dimensions, a cheapest bid manufacturer, and small production runs introduces variations that often require parts be modified to fit together and make the individual machines work. This may seem fine until you need to replace a part or interchange parts with another reloader and you realize the parts are all custom. Additionally, parts that are designed to be modified to fit need to be workable and will not have the hardness of Star's parts that were precision made and heat treated to quality standards established and maintained over decades of manufacturing experience.
I have limited information on the Phelps and Berdan products but what's available is in the Album link at the top of the forum. It may help you spot differences based on the specifications they reference and the pictures they provided in brochures. Most of the clone companies sought to "improve" the powder magazines, handle, etc. It has been reported that Phelps quality depends on where and when the tool was made.
Accessories for powder magazines, adjustable powder slides, Hulme case feeders, Freeloader, and others were marketed to work with Star and Phelps.
Star survived the clones with untarnished quality standards for over 60 years. The copy-cats never seem to gain much reputation worth speaking kindly about.
If someone has first hand experience with a clone, I would like to hear more about it. I know of one person that got a good Phelps and it has stood up to years and years of volume reloading and is still going. Another has sold original Star parts and the buyers discovered they would not fit their clone.
Caution goes to anyone that relies on a decal, blue paint or polished brass and steel to identify a Star or it's condition. There are disreputable people willing to apply blue paint, decals and elbow grease to gussie up an item to sell as a Star reloader. Several clones have appeared on eBay and it pays to take a few steps back and ask hard questions about the details and wonder about anything that is unusual or out of place. Hopefully you will learn to spot a combination of things that just make the package not look right.
Better safe than suckered. Find someone that's been using their Star tool for years and years and shoots what they reload with good results. It's a great way to find a Star and someone to stand for the quality.
Good luck and happy reloading, on your Star!