The Spitzer schedule is an annuity: on a fixed track the payment is the same every month. On variable or indexed tracks it is recalculated when the rate or the index changes, so the payment moves. Directive 329 says a grace loan is repaid by the Spitzer schedule once the grace ends, and the Bank of Israel's uniform compositions use it.
The cost of equal payments is slow principal repayment in the early years. Total interest is higher than with keren shava, but the first payments are lower, which helps you pass the payment-to-income test.
The pitfall is expecting to build equity quickly. If you sell or refinance after a few years, most of what you have paid went to interest.
Example
₪1,000,000 at 4% over 25 years costs about ₪5,278 every month, ₪1,583,500 in total (₪583,500 of interest). In month 1, ₪3,333 is interest and ₪1,945 principal. After 5 years you have paid about ₪316,700 but reduced the principal by only about ₪129,000.