Buying out the Rent Charge on a rental property

Property Investment

Hello colleagues, has anyone got experience of buying out a rentcharge for a one off price..including the letter says 'all legal costs plus a final adjustment rent; with nothing further to pay. Quote valid for 35 days. Price quoted £132.77.

Basically surprised by new demand for rentcharge of £4 pa on a modest inner-city terrace that I've owned for 18 years. Obviously the rentcharge has been sold to an invester [ MCS Property;based in Exeter].

Letter asks for rentcharge [ 13/2/19-24/3/20] of £4. A modest sum which will amount to £16 when I downsize further in 4 years time & selling this HMO.
I could hold out paying that modest sum, or grasp this offer to purchase the rentcharge for £132.77?

So, how useful is it [or how restrictive] to have a rentcharge registered against the property. I can't recall it bothered me,if it was ever mentioned 19 years ago.
Has anyone experienced paying a modest rentcharge on their properties.
I pay a £6 rentcharge pa on two other rentals. They are regularly sold on to other investment outfits. That triggers an offer to me to purchase the rentcharge. Those offers have been £300-£500 & prohibitive. Therefore for those I continue paying the £6's annually.

Whilst this offer is modest, it may be a honey-trap of hidden charges that racks up the original quote of £132. This is why I'm asking for your experiences. I wouldn't ignore the demand for £4, as its not worth my admin time, or nuisance value not to pay this.