SIPPdeal is certainly a little cheaper than HL for dealing and, in my experience, efficient and reliable. It was A LOT cheaper until HL reduced their dealing charges.
Nothing is entirely transparent or presented in an industry-standard form, but SIPPdeal's charges on drawdown do now seem to be higher than HL's and, for most, this will make a lot more difference than the deaing charges:
SIPPdeal's charges
If you set up an income drawdown pension, including paying any lump sum benefits £150 + VAT
If you designate additional funds or request a review of income levels under income drawdown £75 + VAT
Annual income drawdown administration charge to age 75 £75 p.a. + VAT
Annual income drawdown administration charge from age 75 £250 p.a. + VAT
If you transfer out to another UK pension scheme £75 + VAT
If you register for flexible drawdown pension (Applies only on initial set up of flexible drawdown entitlement. This fee is separate, and where relevant in addition, to income drawdown fees.) £75 + VAT
If you close your SIPP through flexible drawdown or trivial commutation £75 + VAT
So, to set up flexible drawdown with SIPPdeal, it will cost £225 + VAT, and then £75 + VAT a year thereafter.
So, over 5 years, SIPPdeal will cost at least £720. Not at all cheap.