WIFI AP as universal repeater (directional antenna)

Hello
I am thinking about buying a wifi access point to act as universal repeater in order to let laptops far away from the wifi modem router to get online as well. However, since I do not know whether this wifi AP will get enough signal with the antenna it brings, I am thinking of replacing the low gain antena(usually 2d it might bring with either a directional or an omnidirectional antenna. The question is: if I use a directional antenna pointing towards the wifi modem router, will still my laptops connected through the wifi AP get enough signal considering the new wifi AP's directional antenna is not going to be pointing towards these laptops but towards the wifi modem router?

That is to say,
Is it a good choice a directional antenna for access points which are not only connected to other wifi access points through wds or wifi universal repeater mode but have to give access to clients such as laptops with wifi cards?
By the way, I am thinking about buying any of these two wifi AP's:

TP-Link TL-WA500G
Conceptronic.net
Which one would you recommend? I guess both of them match my purpose of using it in universal repeater mode, right?

Thanks

Using a directional antenna for this setup will ofcourse affect the signal strength of the laptops as they are facing away from the AP antenna though they might still connect but the signal strength might not be ok.

Using a 15dbi omni antenna will be much better and placing the AP midway between the laptop clients and the router.(visit Cable Assemblies | Connectors | Adapters | Amplifiers | Antennas | Wireless Connectivity Products from L-com.com for antenna types, they have a very good selection of it)

For the radio to use visit Engenius Tech, Inc. and browse thru their selection of outdoor access points/clients/bridges etc.

But note that using repeaters on your network will definitely cut into half your speed and throughput for all wireless clients. Be aware of this.

Does the speed of the clients which get online without using the wifi access point but throught the original wifi modem router also gets decreased?

I thought as well of this choice:

Using a wifi access point in universal repeater mode with more than one antenna in which I would replace one of the built in antennas with a directional antena pointing to the original wifi modemo router. The other(s) built in antennas would still be omnidirectional so they would still provide wireless signal for the AP clients at the same time.

Would this be a good choice? Should this choice work like I described it?