My personal opinion, not a CA.
In secondary market (buy button), there is also price variations due to people buying and selling. Liquidity is low. You might buy at a premium or at a discount. Calculating that is a headache (for me). On taxation,
You can buy in primary market (bids section) and hold till maturity. Less of a headache. Simple 2.5% interest, no tax on capital gains. Stored in demat form if you buy through Kite