The main active deal from Bookbinders Design on this page is the Pebble Grey 5 year diary for $35, available while stock lasts on the website. That fixed price is best if you specifically want that diary now and prefer a guaranteed single item price rather than waiting for a percent off or sitewide promotion. The only other active item is a newsletter signup for special offers and promotions, which does not change the diary price but may deliver future coupons.
If you only want the Pebble Grey 5 year diary: buy it for $35 using the website only offer. The diary is sold at a set price and the page deal applies to selected products while stock lasts, so your final cost for that item is $35 plus any shipping that the site charges at checkout.
If your cart is a small gift order with other full price items: there is currently no sitewide percent off or threshold discount listed, so the diary at $35 remains the only explicit saving on this page. Add the diary at $35 and pay the site shipping and tax terms shown at checkout; signing up to the newsletter will not reduce the current purchase total unless the newsletter email itself later contains a usable coupon.
If you are a first time visitor or want future deals: sign up to the newsletter for special offers and promotions. The signup is useful for future coupons or promotions but it is not a discount that applies automatically to this purchase, and the diary price on the website stays $35 whether you sign up or not.
If you plan to buy multiple gifts or wait for a sale: the current offers list does not show a multi buy, bundle discount, or percent off sale. If you can wait, signing up to the newsletter may notify you of upcoming promotions that could lower the total on larger carts. For now, buying multiple items at full price does not trigger any additional savings from the offers shown here.
When choosing between the options, pick the $35 diary on the website if that exact item is what you want now because it is the only explicit, immediate saving on this page. If you prefer to try for a lower total on a larger order later, sign up to the newsletter and wait for a promotion to arrive by email. There are no stated rules here about stacking, so treat the $35 website price as the concrete cost and any newsletter coupons you later receive as separate offers that may or may not combine according to their own terms.