Completesavings.co.uk - Any Good?

Used for years, they charge £15, you make a purchase at least once a month you get it back, upon submitting proof of purchase. Basically costs you nothing if you buy something no matter how small. 20% off select gift cards 1 per month, few percent all wide range of others with no limit. Only caveat is £250 max monthly cashback claims. Also eBay is normally 10% coupled with bonus nectar points very quickly adds up. Cashback paid automatically via Bacs and in most cases extremely quickly.

Any negative reviews are because it's 2022 our education system is e, too many entitled babies and no one can be bothered to read except they don't seem to struggle with the part that says sign up for free* and receive £16.87 and another £24 off your next purchase at xyz

I use them. I've not had any problems with them. I use parcel2go a lot and get 10% back
It costs £15 per month but you get this back when you make a purchase.* I believe that to get the £15 back you have to use the same retailer you originally signed up with, so join up via someone you make a purchase with at least once a month.
You can buy One4All egift cards and Argos at 20% discount (up to £100 per month) and another £100 from a selection of other companies at a lower rate.
The tracking is reliable and the CS is good.

You just have to remember to claim the £15 'monthly bonus' (it reminds you on the website) otherwise it's pretty much the same as Quidco/TCB but with better rates.
If you use Evri or Parcel2Go regularly I think it's a no brainer.

* This may be because I signed up via a pop up on Parcel2Go and got a bit extra cash for it. You may be able to sign up direct with complete savings, in which case I expect you could get the monthly bonus with any retailer on the site. (edited)