@Mr Keith,
In theory, UBI would be the fiscally conservative answer to a social safety net but:
Depending on the amount proposed if its universal and not means tested it will be more expensive than a means tested program.
Most libertarians and conservatives don't believe it would actually replace other programs but just be added on top.
If it is added on top of other programs, then yes it will fail completely.
Means testing makes it no longer a UBI. Means testing costs money. It is far less expensive in overhead to have a UBI. The added cost of giving a UBI to those who don't need it can be easily compensated for in the tax code. I get an extra $10,000 per year in UBI but pay an extra $10,000 per year in income tax. No extra cost to the government. This does require a more transparent tax code, though, so it is really just pie in the sky dreaming at this point.