I've been checking on this, and bought some Summer Escapes cartridges myself, so I could measure them. It turns out the C-4306 filter is the designated Unicel replacement for the Summer Escapes "A" & "C" cartridges. It is NOT as high quality a cartridge as the C-4607 Intex "C". The 4607 *may* work, but I don't know.

Regarding sizing -- Intex-type pool equipment is undersized in most respects. That's one reason it's so hard to clean them up, after an algae episode.

But, it's a fair trade-off. The original US-made softside pools were very expensive. When you consider that, 8 years ago you might have paid $2,500 for a US made 18' round pool, with the same *functional* utility as this one -- $899 @ Amazon:
Intex 54925EG Ultra Frame Pool Set, 18-Feet by 52-Inch, Gray
And, when you consider that THIS pool -- $349@ Walmart.com:
Summer Escapes Round 18' x 42" Metal-Walled Swimming Pool
is currently on summer clearance for $199@ my local Sams Club, you're definitely getting a deal, even when you consider that probably 10% of Summer Escapes pools have some severe warranty issues.