Buenas,

Pues mirando en Wikipedia he visto que ROOMA ya tiene su entrada.
Lo que he podido verificar es que el DIRT DOG el el mismo que el ROOMBA 400 (antiguo 4000) con la única diferencia de que el DIRT DOG tiene el cepillo inferior diferente...
Aquí os dejo el historial de los modelos:

Models

* First Generation (1G)
o Roomba (2002, improved in 2003, discontinued)
o Roomba Pro (2003, discontinued)
o Roomba Pro Elite, model # 3100, (2003, discontinued)

The first-generation Roombas have three buttons for room size.
Roomba Discovery
Roomba Discovery

* Second Generation (2G) (All 2G Roombas can be updated to 2.1G Roombas)
o Dirt Dog, model # 1100 (Budget model, sweeper only no internal vacuum) (September 2006)[1]
o Roomba, model # 4000, now model # 400 (2006)[2]
o Roomba Red, model # 4100, now model # 410 (2004, improved to 2.1G in 2005) [3]
o Roomba Sage, model # 4105, now model # 416 (2004, improved to 2.1G in 2005) [4]
o Roomba Sage, model # 4110, now model # 416 (identical to # 4105, but includes charging base)
o Roomba Clean Blue, model # 4130, (HSN exclusive model, earliest release of 2.1G Roomba at a special preview price, identical to the 2.1G Sage except for color.(2004, discontinued)
o Roomba Clean Blue, model # 4130, (HSN exclusive model, earliest release of 2.1G Roomba at a special preview price, identical to the 2.1G Discovery except for color) (2004, discontinued)(Although confusing it should be noted both HSN models share the same model number (4130) despite being two very different models.) [5]
o Roomba Silver, model # 4150, (Amazon.com & Target exclusive model, identical to # 4105, except for a special silver finish)
o Roomba Sage for Pets, model # 4170 (2006) [6]
o Roomba Pink Ribbon Edition, model # 4188, (Identical to # 4105 except for color with 20% of the sale price was donated to the Susan G. Komen Breast Cancer Foundation) (2005, discontinued)
o Roomba Discovery, model # 4210, (2004, improved to 2.1G in 2005)[7]
o Roomba Discovery SE, model # 4220, (2004, identical to Discovery 4210 but with different paint and self-charging wall mount; improved to 2.1G in 2005, discontinued)
o Roomba Scheduler, model # 4225, (same as 4230, but sold at Costco)
o Roomba Scheduler, model # 4230, (2005) [8]
o Roomba Scheduler, model # 4260, with Intelli-Bin (auto detection of a full refuse bin) (Sold at Hammacher-Schlemmer)
o Roomba Discovery for Pets (2006)[9]
o Roomba Scheduler with Intelli-Bin (July 2006)[10]

The second-generation Roombas (dubbed "Discovery") replaced their predecessors in July of 2004, adding a larger dust bin, better software that calculates room sizes, fast charging in the home base (or wall hanger in the Discovery SE), and dirt detection. All second-generation Roombas are functionally identical, though some have more or fewer buttons, accessories, or casings, and all featured updated programming after mid 2005. The low-end models continue to be available as of 2007 with new model names.
Third Generation Roomba docked in base station
Third Generation Roomba docked in base station

* Third Generation (according to the Official iRobot Website)
o Roomba 510, 530, 535 (HSN Version), 550 (Costco Version)[11], 560, 570, and 580 (August 2007)[1]

The third-generation 5xx Roomba was introduced in 2007 and features an infrared sensor to detect obstacles, a dock button, and improved mechanical components. Some second-generation models remain on sale, however, as the 4xx series.

Fuente: Wikipedia

Salu2!