Yes, you can use the 4G Jio sim card in Comio C2.
It takes about 4 hours to fully charge the Comio C2. That is because it has huge 4000 mAh battery. If you use any good quality fast charger - the charging time can reduce by almost 35%.
Comio C2 comes with big 4000 mAh battery. It offers talk time of up to 20 hours and standby period of about 500 hours.
No. Since Comio C2 has 4000 mAh big battery and to avoid heating issues, company has used high quality Polycarbonate body.