Why have to change the whole head?

No problem to replace the part. Delivery in 8d. directly in the mailbox. therefore 4/5.
One may regret the price: 50% of full razor and it's one of the cheapest! Given the multiplicity of models just in Remington, I think the management of the stock of spare parts must be more expensive than the parts themselves.
I had to change the heads because I have, by mistake, lost knives. Can not find a single knife. Too bad.