Had Boston Standard over for a few jobs in the past few years. Generally good company and the plumbers are very professional.
Four stars are for price: they charge flat rate fees, which sounds good on paper but in practice can end up costing more than it should (ie 4 different repairs done in 2 hours cost $1000, where if it were hourly it should cost much less). You get what you pay for though and I would use BSP again.