Being a simple and intuitive, but still an entry-level Roomba vacuum, the 650 model has virtually no benefits in comparison with the advanced counterpart, but for the display. It has 8 buttons, including scheduling, docking, spot and default cleaning. It is quiet, long-lasting and reliable. On the contrary, the Roomba 880 is more:
The vacuum is equipped with HEPA filter, backed by Multiroom and iAdapt navigation technologies. Its Virtual Wall system is called Lighthouse, covering large house areas easily. It comes with remote control and dirt extractors. Persistent Pass feature is enabled, as well, so 98% of large and tiny dirt particles are eliminated. Comparing iRobot Roomba 880 vs Roomba 650, I would like to mention that both models are self-charging, coming with beneficial scheduling feature, 3 cleaning modes, pet-friendly, suitable for all floor surface types, but for thick carpets. Roomba 880 still has no Carpet Boost feature.
The vacuums are similar by design, low-profile, differing by the displays and the buttons. Meanwhile, the 880 model is more lightweight, the Roomba 650 is more compact.
Paralleling Roomba 650 vs 880, I would say that the basic model is commonly more affordable. Thus, the 650 model is one of the most popular, coming with an incredibly high rating. Its advanced counterpart is also a bestseller that is rated high.
Being an entry-level model, Roomba 650 is safe, reliable and simple to program. It is pet-friendly, suitable for all floor surface types. It comes with great, intuitive display, offering the useful scheduling opportunity. Additionally, backed by iAdapt and Virtual Wall technologies, the vacuum is quite good at navigation. So, it is recommended for small houses, pet owners and beginners.
Belonging to one of the advanced, 800 series, the vacuum is powerful, efficient in dirt detection and debris extraction, accurate in navigation. It is self-charging, coming with the beneficial HEPA filter, being suitable for pet owners and the people that suffer from allergic diseases. Due to multiroom technology, it is recommended for large house owners. Additionally, due to rubber extractors, the vacuum is virtually maintenance-free. So, I would prefer this model if I could afford it.