Must I get this agreement registered or not?

I am a Naredeco Certified Realtor. One of my client's land had been acquired 50 years back. According to him no compensation received. I checked the records and found him right. Now he has offered to hire me either to get the land back or get the compensation from the Govt. To which I have agreed upon. I have prepared an agreement, The gist is, he will pay me a certain percentage of the benefits, whatsoever he gets from the Govt. If he gets back the same land back or any other land, he will sell this property in the open market and then will pay my fee and if he gets some cash in compensation then he will pay my fee on the same day of the receipt. Now the dilemma is , should I get this agreement registered or even the unregistered one will suffice? I tried to understand by researching on internet and got this--- Indian Registration Act 1908 17. Documents of which registration is compulsory (1) The following documents shall be registered, if the property to which they relate is situate in a district in which, and if they have been executed on or after the date on which, Act No. XVI of 1864, or the Indian Registration Act, 1866, or the Indian Registration Act, 1871, or the Indian Registration Act, 1877 or this Act came or comes into force, namely:- (b) other non-testamentary instruments which purport or operate to create, declare, assign, limit or extinguish, whether in present or in future, any right, title or interest, whether vested or contingent, of the value of one hundred rupees, and upwards, to or in immovable property. BUT COULD MAKE NO HEAD NO TAIL. KINDLY GUIDE.