Domestic coffee roasters are usually 'fluid-bed', barrel or 'stirrer' type.
- Popcorn poppers and most low-end purpose built roasters are fluid-bed. That is you agitate the beans by pumping hot air to roast the beans.
- Barrel types have a rotating barrel with fins inside to agitate the beans.
- Stirrer types have a pot and arms inside that are turned to stir the bean ensuring an even roast.
Upgrading from a popper to another fluid bed usually just buys you some convenience and increased roasting capacity. That being said, I had an iRoast 2 fluid-bed and that lasted at least 2 years. It was still functioning when I upgraded so it probably still works. So it may also be overall cheaper.
IMO, it's more worthwhile to upgrade to a barrel or stirrer type like the Behmor or the iCoffee. They take longer to roast, but you can achieve much better roasts and they have more capacity than fluid-beds.
Edit: Differences between roasters
Just a note between the differences in roasters.
Fluid-beds tend to roast very quickly. 10-15 mins total roast time. But this means that the outside of the bean roasts first and the inside is often lighter. The result is often a bit more acidic or 'bright'. The forced air however, does disperse smoke very quickly and it's a bit cleaner. It still has the capacity to set off your fire alarm.
More traditional designs tend to have longer roast times. I clock about 28 minutes. The slower process gives you a bean that has the same colour inside and out. Anecdotally, I would say most people prefer this. Many of the barrel type also produce a lot of smoke and not suitable for indoor roasting. However, the models I mentioned - the Behmor and the iCoffee - have after burners. This means they actively vent the smoke through a stage that burns up the access smoke and are suitable for indoor roasting.