Does not work at all, useless !!!

I was so glad to find this plugin, which is optimized for booking Hostel rooms.
BUT this plugin does not work at all:

1. The overview screen shows several SQL errors:
Notice: Undefined variable: currency_symbol in
– backend-calendar.php on line 110
– backend-calendar.php on line 112
– backend-calendar.php on line 114
– backend-calendar.php on line 131

2. Rooms cannot be created
Nothing happens when I create a news room. The page reloads with the form blank. Neither a message nor any rooms shown.

3. Settings cannot be saved
After clicking SAVE there is only a javascript alert which shows the message There was a problem saving the settings, please try again..

4. Orders
Errors
– Notice: Undefined variable: current_year in /view-delete-orders.php on line 212
– Notice: Undefined variable: current_month in /view-delete-orders.php on line 212
– Notice: Undefined variable: second_month in /view-delete-orders.php on line 212
– WordPress-Database-Error: [You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘AND (month = OR month = )’ at line 1]
SELECT * FROM wp_hostel_booking_orders WHERE year = AND (month = OR month = )

At the end of the day this plugin is completely useless.
One more question: Why don’t you use a custom posttype for the rooms?