The numbers
A 2-bed flat on a corporate let runs £1,500-£2,800/month depending on city, fully furnished. A TNS whole-house at the monthly rate (20% off the nightly) is £3,000-£4,500/month for a 4-person crew. If you've got 2 people, the AST is cheaper. If you've got 4+, the serviced house is.
The hidden costs of an AST
Council tax (£100-£250/month). Utilities (£200-£400/month). WiFi setup (£30 setup + £30/month). Furnishings if the let is unfurnished. By the time you've added it all up, that 'cheap' £1,500 let costs £2,200-£3,000/month all-in.
Flexibility matters
The AST locks you into 6 months minimum. Half of contracts end early. A serviced arrangement lets you walk out with a week's notice. That flexibility has real financial value.