At my base, pax are bussed to the A/C. But speedy boarding usually works perfectly! There is a nice thick red rope that separates SB and SA pax from the rest of the scrum. This section is opened first, and then once pax are safely up the stairs, the rest of the bus doors open.
The major problems happen when SA or Wheelchair pax 'appear' at the last minute, but in fairness it happens to me only about once or twice a year and it's not necessarily ground-crew's fault.
Redsnail has some good tips
Dolly, My understanding of the SB service is that you are
not guaranteed your choice of seat. Read below from easyJet website (Bold added by me).
Speedy Boarding is a new service from easyJet that guarantees you’ll be amongst the first people called to board your flight whenever you checked in.... When the gate opens, you’ll be called to board first.... So Speedy Boarders have the best chance of being first on board with the first choice of seats!
So, like all contractual agreements, read what it says, not what you want it to say.