A dev agency builds what you tell them to build, well and on a defined timeline, usually £15,000-£40,000+ for an MVP depending on scope and location. A fractional CPO first decides what should be built — through discovery and validation — and then often builds it directly or oversees the build, typically £12,000-£25,000 for a six-week validated MVP. The right choice depends on whether your bottleneck is capacity or clarity.
Most founders who come to me after a failed first MVP attempt didn't have a build problem. They had a spec problem: they briefed an agency to build the wrong thing very well.
What an agency is good at
Agencies are strong when you already know precisely what you want built — you've validated the problem, you have wireframes or a detailed spec, and you need reliable engineering capacity to execute it on a schedule. Good agencies bring project management discipline, a broader bench of specialist skills (native mobile, complex integrations), and predictable delivery cadences.
Where they structurally can't help is deciding what to build in the first place. An agency's incentive is to deliver the brief accurately, not to challenge whether the brief is right — and most agencies won't push back hard on scope because that's not what they're being paid to do.
What a fractional CPO is good at
A fractional CPO runs the validation work before a single line of code gets written — customer interviews, competitive scoping, defining the one user journey that matters — and then either builds the MVP directly using tools like Lovable or Cursor, or writes a spec tight enough that whoever builds it can't drift from what was validated.
The advantage is a single accountable owner across the whole path from idea to shipped product, rather than a handoff between a strategy phase and a build phase that too often loses fidelity in translation.
Cost comparison
A UK dev agency MVP build typically runs £15,000-£40,000+ over eight to fourteen weeks, often billed as a fixed project fee or day rate for a small team (a PM, a designer, one to two developers). This usually excludes discovery — agencies assume you arrive with a validated brief, or charge separately for a discovery sprint.
A fractional-CPO-led MVP build, including discovery, typically runs £12,000-£25,000 over six weeks, because it's usually one senior operator working with AI-assisted build tools rather than a multi-person agency team, and because the scope has already been ruthlessly cut down to a single validated workflow before build starts.
The failure mode of each path
Agencies fail founders most often by building a well-engineered version of an unvalidated idea — the product works exactly as specced and nobody wants it. Fractional CPOs fail founders most often when they're stretched too thin across too many clients to keep momentum on delivery, or when the founder expects full-time availability from a two-day-a-week engagement.
Neither failure mode is really about competence; it's about matching the engagement type to what your company actually needs at that moment.
A blended approach that often works
Some founders use a fractional CPO to run discovery and validation, produce a tight spec and a working prototype, and then hand that spec to an agency (or an in-house engineer) for the heavier build work — using each party for what they're structurally best at. This works particularly well when the MVP needs specialist engineering (complex integrations, native mobile) that goes beyond what a solo fractional CPO can build quickly with no-code or AI-assisted tools.
The key is making sure whoever runs discovery stays involved through build, so the validated insight doesn't get lost in a handover document.
How to decide for your MVP
If you can write a tight, validated one-page brief today — user, problem, wedge, single metric — an agency can likely execute it well. If you can't write that brief with confidence, you have a validation problem, not a build problem, and a fractional CPO is the better starting point. This is exactly why the Crossley Method separates Validate and Prototype from Build MVP as distinct stages: skipping straight to a build engagement before those earlier stages are done is the single most common way founders waste an MVP budget, whichever route — agency or fractional CPO — they eventually choose.
Frequently asked questions
- Is it cheaper to use an agency or a fractional CPO to build an MVP?
- A fractional-CPO-led build, including discovery, is often cheaper at £12,000-£25,000 for six weeks, versus £15,000-£40,000+ for a typical agency MVP build over eight to fourteen weeks, largely because agency pricing usually excludes discovery.
- Can a fractional CPO build an MVP without an agency?
- Yes, for most SaaS MVPs a fractional CPO can build directly using AI-assisted tools like Lovable or Cursor, particularly when the scope is a single validated workflow rather than complex native mobile or heavy integration work.
- When should you use an agency instead of a fractional CPO?
- When you already have a validated, tightly specced brief and need reliable engineering capacity — especially for specialist work like native mobile apps or complex third-party integrations — an agency is often the better fit.
- What's the biggest risk of going straight to an agency for an MVP?
- Building a well-executed version of an unvalidated idea. Agencies build what's specced; they typically don't challenge whether the underlying problem or user need has actually been validated first.