I did my DAS straight off. As I wanted to use it on longer journeys, a 125 was never going to cut the mustard, and as I'm in for the long haul I figured there's no point faffing around! The school I learnt with did fixed-price DAS courses, so no risk of an open-ended number of lessons, and I passed Mod2 within 6 weeks of the CBT, having had about 14 hours of lessons and no practice in-between. I've driven for 12 years and ride pedal bikes quite a bit, both of which really helped in terms of road awareness and the assumption that all other road users are actively trying to kill me, so I found it relatively easy to learn, but it's different for everyone. Also, as 125s are so popular to steal, it might be worth playing around on an insurance comparison site to see what the difference is between a 125 and 500-600cc bigger bike, if you have any idea what sort of bike you might want. Personally, if you're wanting bigger bikes then I'd go straight for the DAS, but it depends on both your budget and also general confidence on the road as to how quickly you might pass.