Which is better for walking 18 holes?

The FootJoy Flex. It is lighter and softer underfoot, so it tires your feet less on a long walk. The S-Casual is the better pick if the course is wet or you want more support.

Are the FootJoy Flex shoes waterproof?

No. The mesh upper is breathable but lets water through in rain or heavy dew. The ECCO S-Casual has an ECCO-TEX membrane and stays dry.

The ECCO S-Casual. Leather and the direct-injected sole hold their shape longer, while the Flex's soft EVA midsole compresses with heavy use.

Is the S-Casual worth stepping up to over the Flex?

If you play in wet conditions or want a shoe that stays supportive over many seasons, yes. If you mostly play dry summer rounds and want light comfort, the Flex is enough.

Do the FootJoy Flex run true to size?

They generally run true to size, and the wide option helps players with broader feet. The S-Casual also runs true but comes in standard width only.

Which has better grip?

The ECCO S-Casual. Its roughly 100 TPU traction bars and 800 traction angles give more bite than the Flex's Versa-Trax spikeless outsole.

FootJoy Flex Golf Shoes vs ECCO Golf S-Casual

The FootJoy Flex is a light, soft, spikeless shoe built for walking and casual rounds in dry weather. The ECCO S-Casual is the sturdier, waterproof leather option with a washable insole and a more locked-in feel. Owners of the Flex praise comfort out of the box but note the mesh soaks through in wet grass; S-Casual buyers accept a heavier, firmer shoe for all-weather play and longer life.

Choose the FootJoy Flex if you walk most rounds, want a soft flexible feel from the first wear, and play mostly in dry conditions.
Choose the ECCO S-Casual if you play year-round, want a waterproof leather shoe that holds its shape, and value a washable insole.

Prices

FootJoy Flex Golf Shoes: $89.95 at Zappos (last seen Nov 9)
ECCO Golf S-Casual: $89.99 at Scheels (last seen Nov 9)
Difference: the FootJoy Flex Golf Shoes is $0.04 cheaper than the ECCO Golf S-Casual at the latest prices (Nov 9)