Summarise a Buy-to-Let Mortgage Illustration

A buy-to-let illustration looks fine until you do the yield maths, which is exactly the bit most people skip. This pulls the core numbers, loan, LTV, initial rate, monthly interest-only payment, revert rate, total cost, then works the yield against your estimated rent. You find out if the deal is viable or just a way to lose money slowly with a tenant in it.

<context>
You have received a mortgage illustration for a buy-to-let property purchase and need to assess whether the deal is financially viable before proceeding.
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<task>
**Step 1: Extract the core numbers**
Identify: loan amount, LTV percentage, initial interest rate, monthly interest-only payment, revert rate, and total cost over the initial period.

**Step 2: Calculate yield viability**
Using [estimated monthly rental income], calculate whether the rental yield covers the mortgage interest at a 125% or 145% stress test.

**Step 3: Assess fees and true cost**
Add arrangement fee, valuation fee, and legal costs to arrive at the true upfront cost. State the APR in plain terms.

**Step 4: Summarise the risk**
Identify the two biggest risks if rental income drops or interest rates rise further.
</task>

<output_format>
- Step outputs with clear numbers
- A viability verdict: Go / Proceed with caution / Reconsider
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