In the fitness equipment world as with most electronics, they always seem to be upgrading, and of course telling you that you will lose out if you do not upgrade. By taking a look at three models of a recumbent Star Trac Exercise bike, you can see they provide a good example of the decision making process. They have recumbent bike models that are 8710, 8720, and 8730.
One thing to note is the price range. Star Trac pricing is generally in the mid range which is around $1200-$2200 price range. Some larger companies will have models in all three levels, budget, mid-range and premium top of the line So you need to be sure your comparisons are within the same price and style of bike. If you see an entirely different number and even how they word the name, you can expect an entirely different series and even the pricing. So it is worth checking the website to see where things are.
In any case, here we are discussing three obviously similar bikes. So the first thing to look at is the lowest model number as it is usually the lower price. When there are three models like this, it is not unusual to find the lowest model is hard to find. It might be listed as out of stock, or a long shipping time, or you might only be able to find it with used vendor sites or on eBay. You will be able to get a good sales price this way, but you also take the risk of them discontinuing the model, so parts etc are harder to get.
When there has been a recent upgrade, both bikes will still be available, so you need to look at the features and see if you really need the upgraded features. They do not make it easy for you since of course they will want you to get the more expensive bike. In some companies the difference is with a color LCD displays or it might be larger or have more bells and whistles. In this case the two Star Trac exercise bike models 8720 and 8730 have pretty much the same display, and built-in pro grams. So you look further.
The upgraded version had movable arm rests and a feature on the handlebars where you can control the adjustments to the workout with a toggle bar. These are two very convenient items and there are those that it could be a deal breaker. Others could care less.
Sometimes just a look at the pictures will tell you something. The upgrade model of this Star Trac exercise bike, model 8730 had a head support that the 8720 does not have. This would add in the comfort when using the recumbent position to exercise. There were other design changes, but the over all dimensions did not change. The bottom line then will be either lower price or preferring the newest and most up to date model. After all of that, it boils down to personal preference.