I've stopped by here several times as it's very near my apartment in Paris, and I've enjoyed everything I've gotten so far. This Eric Kayser is conveniently located just a short walk from the Argentine metro stop in the 16th arrondissement (line 1). It has very generous hours, and is open 7 days a week. This past year it was also open on some major holidays, including Christmas and New Year's, albeit with reduced hours.
Since this is a chain bakery, they have a wider range of products on sale than a typical local boulangerie/pâtisserie, including macarons, packaged chocolates, ice cream, salad/grain bowls, and a couple different sandwiches. Around Christmas they had both full-size bûches (Yule log cakes) as well as mini "bûchettes" that were just for 1 person, in a couple different flavors. Other seasonal offerings included loaves of pain d'épices and galettes des rois (again, both full-sized and single-sized).
However, I found their normal bakery offerings--breads, pastries, tarts--to be comparable to other local boulangeries/pâtisseries in terms of both quality and price. For example, baguettes came in at 1€ apiece, demi-baguettes at 0,55€, croissants and pains au chocolat at around 1,25-1,35€ apiece, and bags of 10 or so chouquettes for like 2,50€. Some of their fancier pastries/tarts were a bit more expensive than those at some of the other pâtisseries, but often not by much, and they did seem to be made with a high level of care and artistry that might've warranted it (especially the bûchettes at Christmas). This location is therefore definitely a solid choice for everyday staples, but also a place to get occasional, fancier treats.
The staff are efficient and polite; often there's a line in the morning or just before lunch, but they get through the customers really quickly. Credit cards are accepted and there does not appear to be a credit card minimum; I have paid for a 0,55€ demi-baguette with a card without issues. There are a few tables inside if you want to have your order to stay, but most seem to take theirs to-go. Definitely worth a visit if you're in the area! read more