first try to find APC 800VA UPS. it'll cost lot more but worth the investment. but do some research before settling for any particular one. most of the time some specific models are known to have problems in the entire lineup of good products which we trust blindly.
can't say much about Luminous. do check (online) under what condition they offer warranty on the battery. cause its the battery thats most likely needs to be changed within the 2yr of operation. they may show you some exceptional cases under which they won't honor the warranty.
APC 800VA is not available in market.. may be APC is coming up with new modified model.. as i got to knw from APC retailer in New Delhi
so if u can w8 for a month.. then it would be great..
otherwise you can go for APC650VA.. if it can fulfill your needs.