Nice!

You also get 3 months PS+ free

Just seen its in the promotion at the top of the page, it says :

From the 1st of March, when you buy a PS4 console among the ones below, you will receive a code to redeem a 3 month free PlayStation Plus membership. This offer ends at 23:59 on 31st of March.
The offer only applies to items sold by Amazon at the website http://www.amazon.co.uk . The offer does not apply to purchases made from Amazon's Warehouse Deals or from third-party sellers on Amazon Marketplace.
This offer is only valid on your UK PlayStation account
Postage and packing will be applied to each item in accordance with Amazon's standard delivery rates and policies or the participating third-party seller's standard delivery rates and policies, as applicable.
The offer is valid only for the products displayed on https://www.amazon.co.uk/l/12621367031.
Each customer can claim up to a maximum of one offer.
Unless otherwise specified on the landing page of the relevant promotion, the offer may not be used on pre-existing orders or in conjunction with any other offer.
Each customer can claim up to a maximum of 1 code.
Please note that while a promotional reward will automatically be applied to your account, you will need to enter a promotional code during checkout for it to apply. Any promotional reward added to your Amazon.co.uk account by Amazon expires on 31 December 2020 unless otherwise specified by Amazon. When paying for an order with a promotional code or promotional reward you will have to add the relevant item(s) to your Shopping Basket and complete your order via checkout. If you use our 1-Click ordering method, any promotional claim code or promotional reward will not apply to your order.
If you have applied a promotional code to your account but have not completed checkout of a relevant order, the code does not need to be re-entered when completing checkout for another order that qualifies for the same offer.
If your order value exceeds the value of the promotional code or promotional reward, you must pay the balance either by credit or debit card, or by using Amazon.co.uk Gift Cards. Unlike Amazon.co.uk Gift Cards, you will not be able to view any unused promotional codes or promotional rewards in the Your Account section of http://www.amazon.co.uk.
Promotional codes and promotional rewards have no cash redemption value and are not transferable or assignable.
If you place an order using a promotional reward and then return that order, the promotional reward cannot be refunded or re-used.
If you place an order using a promotional code and then return or cancel that order, the promotional code cannot be refunded or re-used.
Unless otherwise specified on the landing page of the offer or by Amazon:
(i) promotional codes or promotional rewards cannot be used on existing orders; and
(ii) only one promotional code or promotional reward can be redeemed per order.
If an offer is specific to a particular item, then a promotional code or promotional reward can only be redeemed against that item.
You will receive a promotional code via e-mail from Amazon within 1 day of dispatch of a qualifying purchase. If you cancel the order before this deadline, you will not receive the promotional code.
The offer is subject to availability and may be withdrawn or amended without notice. The offer has no cash alternative.
Offer is non-transferable and may not be resold.
Amazon's Conditions of Use & Sale apply..

Can anyone see anything else that may invalidate this offer?

Anyway just used £30 on my gift credit I got from Quidco, so got it down to £170, I will just sell the PS4 slim and Dual Shock and keep the PS Plus and Horizon, getting them free essentially

They're giving an extra £5 when you top up your wallet by £100 too (not sure if targeted or everyone) so that could be another fiver saved.

Account specific
Thank you for your interest in Top Up.

Unfortunately, you are not eligible for this offer.

Bloody hell... thought the deal the other day was good! Guess I'll be fishing the boxes out of the bin to return lol

Is argos not offering the slim version for the same price.