I flew recently to SE Asia with Air France on the way out and KLM on the way back. There was no business class upgrade availability on the AF flight, and I didn't fancy using 90,000 Flying Blue miles for an upgrade to business on the KLM flight given it was a daytime flight, so decided just to make the best of Economy. Paid for an exit seat both ways, and thought it absolutely worthwhile for the extra legroom and direct aisle access, even if the KLM standard fee for this is a bit pricey. Interestingly, there's a discount on such seat fees for Flying Blue holders, amount depending upon your tier, ranging from 10% for Ivory up to 50% for Gold. For fun, I also tried the 'A la carte' menu option (I went for 'Menu Tradition') on the AF flight, and thought that was worth the price too. It was served on a regular Economy meal tray, but the food was a bit different and tastier than a standard meal. Such options are available on AF flights out of Paris (though not on flights returning to Paris, I think). On the way back, just had a regular KLM Economy meal, but was pleasantly surprised with the quality.